[PATCH v3 00/13] kmem controller for memcg.

[PATCH v3 00/13] kmem controller for memcg.

[Glauber Costa]

Hi,

This is the first part of the kernel memory controller for memcg. It has been
discussed many times, and I consider this stable enough to be on tree. A follow
up to this series are the patches to also track slab memory. They are not
included here because I believe we could benefit from merging them separately
for better testing coverage. If there are any issues preventing this to be
merged, let me know. I'll be happy to address them.

*v3:
	- Changed function names to match memcg's
	- avoid doing get/put in charge/uncharge path
	- revert back to keeping the account enabled after it is first activated

The slab patches are also mature in my self evaluation and could be merged not
too long after this. For the reference, the last discussion about them happened
at http://lwn.net/Articles/508087/. Patches for that will be sent shortly, and
will include the documentation for this.

Numbers can be found at https://lkml.org/lkml/2012/9/13/239

A (throwaway) git tree with them is placed at:

	git://git.kernel.org/pub/scm/linux/kernel/git/glommer/memcg.git kmemcg-stack

A general explanation of what this is all about follows:

The kernel memory limitation mechanism for memcg concerns itself with
disallowing potentially non-reclaimable allocations to happen in exaggerate
quantities by a particular set of processes (cgroup). Those allocations could
create pressure that affects the behavior of a different and unrelated set of
processes.

Its basic working mechanism is to annotate some allocations with the
_GFP_KMEMCG flag. When this flag is set, the current process allocating will
have its memcg identified and charged against. When reaching a specific limit,
further allocations will be denied.

One example of such problematic pressure that can be prevented by this work is
a fork bomb conducted in a shell. We prevent it by noting that processes use a
limited amount of stack pages. Seen this way, a fork bomb is just a special
case of resource abuse. If the offender is unable to grab more pages for the
stack, no new processes can be created.

There are also other things the general mechanism protects against. For
example, using too much of pinned dentry and inode cache, by touching files an
leaving them in memory forever.

In fact, a simple:

while true; do mkdir x; cd x; done

can halt your system easily because the file system limits are hard to reach
(big disks), but the kernel memory is not. Those are examples, but the list
certainly don't stop here.

An important use case for all that, is concerned with people offering hosting
services through containers. In a physical box we can put a limit to some
resources, like total number of processes or threads. But in an environment
where each independent user gets its own piece of the machine, we don't want a
potentially malicious user to destroy good users' services.

This might be true for systemd as well, that now groups services inside
cgroups. They generally want to put forward a set of guarantees that limits the
running service in a variety of ways, so that if they become badly behaved,
they won't interfere with the rest of the system.

There is, of course, a cost for that. To attempt to mitigate that, static
branches are used to make sure that even if the feature is compiled in with
potentially a lot of memory cgroups deployed this code will only be enabled
after the first user of this service configures any limit. Limits lower than
the user limit effectively means there is a separate kernel memory limit that
may be reached independently than the user limit. Values equal or greater than
the user limit implies only that kernel memory is tracked. This provides a
unified vision of "maximum memory", be it kernel or user memory. Because this
is all default-off, existing deployments will see no change in behavior.


Glauber Costa (11):
  memcg: change defines to an enum
  kmem accounting basic infrastructure
  Add a __GFP_KMEMCG flag
  memcg: kmem controller infrastructure
  mm: Allocate kernel pages to the right memcg
  res_counter: return amount of charges after res_counter_uncharge
  memcg: kmem accounting lifecycle management
  memcg: use static branches when code not in use
  memcg: allow a memcg with kmem charges to be destructed.
  execute the whole memcg freeing in rcu callback
  protect architectures where THREAD_SIZE >= PAGE_SIZE against fork
    bombs

Suleiman Souhlal (2):
  memcg: Make it possible to use the stock for more than one page.
  memcg: Reclaim when more than one page needed.

 Documentation/cgroups/resource_counter.txt |   7 +-
 include/linux/gfp.h                        |  10 +-
 include/linux/memcontrol.h                 |  99 ++++++
 include/linux/res_counter.h                |  12 +-
 include/linux/thread_info.h                |   2 +
 kernel/fork.c                              |   4 +-
 kernel/res_counter.c                       |  20 +-
 mm/memcontrol.c                            | 519 +++++++++++++++++++++++++----
 mm/page_alloc.c                            |  35 ++
 9 files changed, 628 insertions(+), 80 deletions(-)

-- 
1.7.11.4

[PATCH v3 01/13] memcg: Make it possible to use the stock for more than one page.

[Glauber Costa]

From: Suleiman Souhlal <ssouhlal-HZy0K5TPuP5AfugRpC6u6w@public.gmane.org>

We currently have a percpu stock cache scheme that charges one page at a
time from memcg->res, the user counter. When the kernel memory
controller comes into play, we'll need to charge more than that.

This is because kernel memory allocations will also draw from the user
counter, and can be bigger than a single page, as it is the case with
the stack (usually 2 pages) or some higher order slabs.

[ glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org: added a changelog ]

Signed-off-by: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
Acked-by: David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
Acked-by: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
---
 mm/memcontrol.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 795e525..9d3bc72 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2034,20 +2034,28 @@ struct memcg_stock_pcp {
 static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
 static DEFINE_MUTEX(percpu_charge_mutex);
 
-/*
- * Try to consume stocked charge on this cpu. If success, one page is consumed
- * from local stock and true is returned. If the stock is 0 or charges from a
- * cgroup which is not current target, returns false. This stock will be
- * refilled.
+/**
+ * consume_stock: Try to consume stocked charge on this cpu.
+ * @memcg: memcg to consume from.
+ * @nr_pages: how many pages to charge.
+ *
+ * The charges will only happen if @memcg matches the current cpu's memcg
+ * stock, and at least @nr_pages are available in that stock.  Failure to
+ * service an allocation will refill the stock.
+ *
+ * returns true if succesfull, false otherwise.
  */
-static bool consume_stock(struct mem_cgroup *memcg)
+static bool consume_stock(struct mem_cgroup *memcg, int nr_pages)
 {
 	struct memcg_stock_pcp *stock;
 	bool ret = true;
 
+	if (nr_pages > CHARGE_BATCH)
+		return false;
+
 	stock = &get_cpu_var(memcg_stock);
-	if (memcg == stock->cached && stock->nr_pages)
-		stock->nr_pages--;
+	if (memcg == stock->cached && stock->nr_pages >= nr_pages)
+		stock->nr_pages -= nr_pages;
 	else /* need to call res_counter_charge */
 		ret = false;
 	put_cpu_var(memcg_stock);
@@ -2346,7 +2354,7 @@ again:
 		VM_BUG_ON(css_is_removed(&memcg->css));
 		if (mem_cgroup_is_root(memcg))
 			goto done;
-		if (nr_pages == 1 && consume_stock(memcg))
+		if (consume_stock(memcg, nr_pages))
 			goto done;
 		css_get(&memcg->css);
 	} else {
@@ -2371,7 +2379,7 @@ again:
 			rcu_read_unlock();
 			goto done;
 		}
-		if (nr_pages == 1 && consume_stock(memcg)) {
+		if (consume_stock(memcg, nr_pages)) {
 			/*
 			 * It seems dagerous to access memcg without css_get().
 			 * But considering how consume_stok works, it's not
-- 
1.7.11.4

Re: [PATCH v3 01/13] memcg: Make it possible to use the stock for more than one page.

[Johannes Weiner]

On Tue, Sep 18, 2012 at 06:03:58PM +0400, Glauber Costa wrote:
> From: Suleiman Souhlal <ssouhlal@FreeBSD.org>
> 
> We currently have a percpu stock cache scheme that charges one page at a
> time from memcg->res, the user counter. When the kernel memory
> controller comes into play, we'll need to charge more than that.
> 
> This is because kernel memory allocations will also draw from the user
> counter, and can be bigger than a single page, as it is the case with
> the stack (usually 2 pages) or some higher order slabs.
> 
> [ glommer@parallels.com: added a changelog ]
> 
> Signed-off-by: Suleiman Souhlal <suleiman@google.com>
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> Acked-by: David Rientjes <rientjes@google.com>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Acked-by: Michal Hocko <mhocko@suse.cz>

Independent of how the per-subtree enable-through-setting-limit
discussion pans out, we're going to need the charge cache, so:

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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[PATCH v3 02/13] memcg: Reclaim when more than one page needed.

[Glauber Costa]

From: Suleiman Souhlal <ssouhlal-HZy0K5TPuP5AfugRpC6u6w@public.gmane.org>

mem_cgroup_do_charge() was written before kmem accounting, and expects
three cases: being called for 1 page, being called for a stock of 32
pages, or being called for a hugepage.  If we call for 2 or 3 pages (and
both the stack and several slabs used in process creation are such, at
least with the debug options I had), it assumed it's being called for
stock and just retried without reclaiming.

Fix that by passing down a minsize argument in addition to the csize.

And what to do about that (csize == PAGE_SIZE && ret) retry?  If it's
needed at all (and presumably is since it's there, perhaps to handle
races), then it should be extended to more than PAGE_SIZE, yet how far?
And should there be a retry count limit, of what?  For now retry up to
COSTLY_ORDER (as page_alloc.c does) and make sure not to do it if
__GFP_NORETRY.

[v4: fixed nr pages calculation pointed out by Christoph Lameter ]

Signed-off-by: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
Reviewed-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
Acked-by: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
---
 mm/memcontrol.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9d3bc72..b12121b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2232,7 +2232,8 @@ enum {
 };
 
 static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
-				unsigned int nr_pages, bool oom_check)
+				unsigned int nr_pages, unsigned int min_pages,
+				bool oom_check)
 {
 	unsigned long csize = nr_pages * PAGE_SIZE;
 	struct mem_cgroup *mem_over_limit;
@@ -2255,18 +2256,18 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	} else
 		mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
 	/*
-	 * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch
-	 * of regular pages (CHARGE_BATCH), or a single regular page (1).
-	 *
 	 * Never reclaim on behalf of optional batching, retry with a
 	 * single page instead.
 	 */
-	if (nr_pages == CHARGE_BATCH)
+	if (nr_pages > min_pages)
 		return CHARGE_RETRY;
 
 	if (!(gfp_mask & __GFP_WAIT))
 		return CHARGE_WOULDBLOCK;
 
+	if (gfp_mask & __GFP_NORETRY)
+		return CHARGE_NOMEM;
+
 	ret = mem_cgroup_reclaim(mem_over_limit, gfp_mask, flags);
 	if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
 		return CHARGE_RETRY;
@@ -2279,7 +2280,7 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	 * unlikely to succeed so close to the limit, and we fall back
 	 * to regular pages anyway in case of failure.
 	 */
-	if (nr_pages == 1 && ret)
+	if (nr_pages <= (1 << PAGE_ALLOC_COSTLY_ORDER) && ret)
 		return CHARGE_RETRY;
 
 	/*
@@ -2414,7 +2415,8 @@ again:
 			nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
 		}
 
-		ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, oom_check);
+		ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, nr_pages,
+		    oom_check);
 		switch (ret) {
 		case CHARGE_OK:
 			break;
-- 
1.7.11.4

Re: [PATCH v3 02/13] memcg: Reclaim when more than one page needed.

[Johannes Weiner]

On Tue, Sep 18, 2012 at 06:03:59PM +0400, Glauber Costa wrote:
> From: Suleiman Souhlal <ssouhlal@FreeBSD.org>
> 
> mem_cgroup_do_charge() was written before kmem accounting, and expects
> three cases: being called for 1 page, being called for a stock of 32
> pages, or being called for a hugepage.  If we call for 2 or 3 pages (and
> both the stack and several slabs used in process creation are such, at
> least with the debug options I had), it assumed it's being called for
> stock and just retried without reclaiming.
> 
> Fix that by passing down a minsize argument in addition to the csize.
> 
> And what to do about that (csize == PAGE_SIZE && ret) retry?  If it's

Wow, that patch set has been around for a while.  It's been nr_pages
== 1 for a while now :-)

> needed at all (and presumably is since it's there, perhaps to handle
> races), then it should be extended to more than PAGE_SIZE, yet how far?
> And should there be a retry count limit, of what?  For now retry up to
> COSTLY_ORDER (as page_alloc.c does) and make sure not to do it if
> __GFP_NORETRY.
>
> [v4: fixed nr pages calculation pointed out by Christoph Lameter ]
> 
> Signed-off-by: Suleiman Souhlal <suleiman@google.com>
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> Reviewed-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Acked-by: Michal Hocko <mhocko@suse.cz>
> ---
>  mm/memcontrol.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 9d3bc72..b12121b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2232,7 +2232,8 @@ enum {
>  };
>  
>  static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
> -				unsigned int nr_pages, bool oom_check)
> +				unsigned int nr_pages, unsigned int min_pages,
> +				bool oom_check)

I'm not a big fan of the parameter names.  Can we make this function
officially aware of batching and name the parameters like the
arguments that are passed in?  I.e. @batch and @nr_pages?

>  {
>  	unsigned long csize = nr_pages * PAGE_SIZE;
>  	struct mem_cgroup *mem_over_limit;
> @@ -2255,18 +2256,18 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  	} else
>  		mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
>  	/*
> -	 * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch
> -	 * of regular pages (CHARGE_BATCH), or a single regular page (1).
> -	 *
>  	 * Never reclaim on behalf of optional batching, retry with a
>  	 * single page instead.

"[...] with the amount of actually required pages instead."

>  	 */
> -	if (nr_pages == CHARGE_BATCH)
> +	if (nr_pages > min_pages)
>  		return CHARGE_RETRY;

	if (batch > nr_pages)
		return CHARGE_RETRY;

But that is all just nitpicking.  Functionally, it looks sane, so:

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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[PATCH v3 03/13] memcg: change defines to an enum

[Glauber Costa]

This is just a cleanup patch for clarity of expression.  In earlier
submissions, people asked it to be in a separate patch, so here it is.

[ v2: use named enum as type throughout the file as well ]

Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
Acked-by: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
---
 mm/memcontrol.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b12121b..d6ad138 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -385,9 +385,12 @@ enum charge_type {
 };
 
 /* for encoding cft->private value on file */
-#define _MEM			(0)
-#define _MEMSWAP		(1)
-#define _OOM_TYPE		(2)
+enum res_type {
+	_MEM,
+	_MEMSWAP,
+	_OOM_TYPE,
+};
+
 #define MEMFILE_PRIVATE(x, val)	((x) << 16 | (val))
 #define MEMFILE_TYPE(val)	((val) >> 16 & 0xffff)
 #define MEMFILE_ATTR(val)	((val) & 0xffff)
@@ -3921,7 +3924,8 @@ static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
 	struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
 	char str[64];
 	u64 val;
-	int type, name, len;
+	int name, len;
+	enum res_type type;
 
 	type = MEMFILE_TYPE(cft->private);
 	name = MEMFILE_ATTR(cft->private);
@@ -3957,7 +3961,8 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
 			    const char *buffer)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
-	int type, name;
+	enum res_type type;
+	int name;
 	unsigned long long val;
 	int ret;
 
@@ -4033,7 +4038,8 @@ out:
 static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
-	int type, name;
+	int name;
+	enum res_type type;
 
 	type = MEMFILE_TYPE(event);
 	name = MEMFILE_ATTR(event);
@@ -4369,7 +4375,7 @@ static int mem_cgroup_usage_register_event(struct cgroup *cgrp,
 	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
 	struct mem_cgroup_thresholds *thresholds;
 	struct mem_cgroup_threshold_ary *new;
-	int type = MEMFILE_TYPE(cft->private);
+	enum res_type type = MEMFILE_TYPE(cft->private);
 	u64 threshold, usage;
 	int i, size, ret;
 
@@ -4452,7 +4458,7 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
 	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
 	struct mem_cgroup_thresholds *thresholds;
 	struct mem_cgroup_threshold_ary *new;
-	int type = MEMFILE_TYPE(cft->private);
+	enum res_type type = MEMFILE_TYPE(cft->private);
 	u64 usage;
 	int i, j, size;
 
@@ -4530,7 +4536,7 @@ static int mem_cgroup_oom_register_event(struct cgroup *cgrp,
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
 	struct mem_cgroup_eventfd_list *event;
-	int type = MEMFILE_TYPE(cft->private);
+	enum res_type type = MEMFILE_TYPE(cft->private);
 
 	BUG_ON(type != _OOM_TYPE);
 	event = kmalloc(sizeof(*event),	GFP_KERNEL);
@@ -4555,7 +4561,7 @@ static void mem_cgroup_oom_unregister_event(struct cgroup *cgrp,
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
 	struct mem_cgroup_eventfd_list *ev, *tmp;
-	int type = MEMFILE_TYPE(cft->private);
+	enum res_type type = MEMFILE_TYPE(cft->private);
 
 	BUG_ON(type != _OOM_TYPE);
 
-- 
1.7.11.4

Re: [PATCH v3 03/13] memcg: change defines to an enum

[Johannes Weiner]

On Tue, Sep 18, 2012 at 06:04:00PM +0400, Glauber Costa wrote:
> This is just a cleanup patch for clarity of expression.  In earlier
> submissions, people asked it to be in a separate patch, so here it is.
> 
> [ v2: use named enum as type throughout the file as well ]
> 
> Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
> CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
> Acked-by: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>

Should probably be the first in the series to get the cleanups out of
the way :-)

Acked-by: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>

Re: [PATCH v3 03/13] memcg: change defines to an enum

[Glauber Costa]

On 10/01/2012 11:06 PM, Johannes Weiner wrote:
> On Tue, Sep 18, 2012 at 06:04:00PM +0400, Glauber Costa wrote:
>> This is just a cleanup patch for clarity of expression.  In earlier
>> submissions, people asked it to be in a separate patch, so here it is.
>>
>> [ v2: use named enum as type throughout the file as well ]
>>
>> Signed-off-by: Glauber Costa <glommer@parallels.com>
>> CC: Johannes Weiner <hannes@cmpxchg.org>
>> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>> Acked-by: Michal Hocko <mhocko@suse.cz>
> 
> Should probably be the first in the series to get the cleanups out of
> the way :-)
> 
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> 
If you guys want to merge this separately, be my guest =)

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[PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

This patch adds the basic infrastructure for the accounting of the slab
caches. To control that, the following files are created:

 * memory.kmem.usage_in_bytes
 * memory.kmem.limit_in_bytes
 * memory.kmem.failcnt
 * memory.kmem.max_usage_in_bytes

They have the same meaning of their user memory counterparts. They
reflect the state of the "kmem" res_counter.

The code is not enabled until a limit is set. This can be tested by the
flag "kmem_accounted". This means that after the patch is applied, no
behavioral changes exists for whoever is still using memcg to control
their memory usage.

We always account to both user and kernel resource_counters. This
effectively means that an independent kernel limit is in place when the
limit is set to a lower value than the user memory. A equal or higher
value means that the user limit will always hit first, meaning that kmem
is effectively unlimited.

People who want to track kernel memory but not limit it, can set this
limit to a very high number (like RESOURCE_MAX - 1page - that no one
will ever hit, or equal to the user memory)

Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
---
 mm/memcontrol.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 63 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d6ad138..f3fd354 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -265,6 +265,10 @@ struct mem_cgroup {
 	};
 
 	/*
+	 * the counter to account for kernel memory usage.
+	 */
+	struct res_counter kmem;
+	/*
 	 * Per cgroup active and inactive list, similar to the
 	 * per zone LRU lists.
 	 */
@@ -279,6 +283,7 @@ struct mem_cgroup {
 	 * Should the accounting and control be hierarchical, per subtree?
 	 */
 	bool use_hierarchy;
+	bool kmem_accounted;
 
 	bool		oom_lock;
 	atomic_t	under_oom;
@@ -389,6 +394,7 @@ enum res_type {
 	_MEM,
 	_MEMSWAP,
 	_OOM_TYPE,
+	_KMEM,
 };
 
 #define MEMFILE_PRIVATE(x, val)	((x) << 16 | (val))
@@ -1439,6 +1445,10 @@ done:
 		res_counter_read_u64(&memcg->memsw, RES_USAGE) >> 10,
 		res_counter_read_u64(&memcg->memsw, RES_LIMIT) >> 10,
 		res_counter_read_u64(&memcg->memsw, RES_FAILCNT));
+	printk(KERN_INFO "kmem: usage %llukB, limit %llukB, failcnt %llu\n",
+		res_counter_read_u64(&memcg->kmem, RES_USAGE) >> 10,
+		res_counter_read_u64(&memcg->kmem, RES_LIMIT) >> 10,
+		res_counter_read_u64(&memcg->kmem, RES_FAILCNT));
 }
 
 /*
@@ -3946,6 +3956,9 @@ static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
 		else
 			val = res_counter_read_u64(&memcg->memsw, name);
 		break;
+	case _KMEM:
+		val = res_counter_read_u64(&memcg->kmem, name);
+		break;
 	default:
 		BUG();
 	}
@@ -3984,8 +3997,18 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
 			break;
 		if (type == _MEM)
 			ret = mem_cgroup_resize_limit(memcg, val);
-		else
+		else if (type == _MEMSWAP)
 			ret = mem_cgroup_resize_memsw_limit(memcg, val);
+		else if (type == _KMEM) {
+			ret = res_counter_set_limit(&memcg->kmem, val);
+			if (ret)
+				break;
+
+			/* For simplicity, we won't allow this to be disabled */
+			if (!memcg->kmem_accounted && val != RESOURCE_MAX)
+				memcg->kmem_accounted = true;
+		} else
+			return -EINVAL;
 		break;
 	case RES_SOFT_LIMIT:
 		ret = res_counter_memparse_write_strategy(buffer, &val);
@@ -4051,12 +4074,16 @@ static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
 	case RES_MAX_USAGE:
 		if (type == _MEM)
 			res_counter_reset_max(&memcg->res);
+		else if (type == _KMEM)
+			res_counter_reset_max(&memcg->kmem);
 		else
 			res_counter_reset_max(&memcg->memsw);
 		break;
 	case RES_FAILCNT:
 		if (type == _MEM)
 			res_counter_reset_failcnt(&memcg->res);
+		else if (type == _KMEM)
+			res_counter_reset_failcnt(&memcg->kmem);
 		else
 			res_counter_reset_failcnt(&memcg->memsw);
 		break;
@@ -4618,6 +4645,33 @@ static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
 }
 
 #ifdef CONFIG_MEMCG_KMEM
+static struct cftype kmem_cgroup_files[] = {
+	{
+		.name = "kmem.limit_in_bytes",
+		.private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
+		.write_string = mem_cgroup_write,
+		.read = mem_cgroup_read,
+	},
+	{
+		.name = "kmem.usage_in_bytes",
+		.private = MEMFILE_PRIVATE(_KMEM, RES_USAGE),
+		.read = mem_cgroup_read,
+	},
+	{
+		.name = "kmem.failcnt",
+		.private = MEMFILE_PRIVATE(_KMEM, RES_FAILCNT),
+		.trigger = mem_cgroup_reset,
+		.read = mem_cgroup_read,
+	},
+	{
+		.name = "kmem.max_usage_in_bytes",
+		.private = MEMFILE_PRIVATE(_KMEM, RES_MAX_USAGE),
+		.trigger = mem_cgroup_reset,
+		.read = mem_cgroup_read,
+	},
+	{},
+};
+
 static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
 {
 	return mem_cgroup_sockets_init(memcg, ss);
@@ -4961,6 +5015,12 @@ mem_cgroup_create(struct cgroup *cont)
 		int cpu;
 		enable_swap_cgroup();
 		parent = NULL;
+
+#ifdef CONFIG_MEMCG_KMEM
+		WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys,
+					   kmem_cgroup_files));
+#endif
+
 		if (mem_cgroup_soft_limit_tree_init())
 			goto free_out;
 		root_mem_cgroup = memcg;
@@ -4979,6 +5039,7 @@ mem_cgroup_create(struct cgroup *cont)
 	if (parent && parent->use_hierarchy) {
 		res_counter_init(&memcg->res, &parent->res);
 		res_counter_init(&memcg->memsw, &parent->memsw);
+		res_counter_init(&memcg->kmem, &parent->kmem);
 		/*
 		 * We increment refcnt of the parent to ensure that we can
 		 * safely access it on res_counter_charge/uncharge.
@@ -4989,6 +5050,7 @@ mem_cgroup_create(struct cgroup *cont)
 	} else {
 		res_counter_init(&memcg->res, NULL);
 		res_counter_init(&memcg->memsw, NULL);
+		res_counter_init(&memcg->kmem, NULL);
 	}
 	memcg->last_scanned_node = MAX_NUMNODES;
 	INIT_LIST_HEAD(&memcg->oom_notify);
-- 
1.7.11.4

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

On Tue, Sep 18, 2012 at 06:04:01PM +0400, Glauber Costa wrote:
>  #ifdef CONFIG_MEMCG_KMEM
> +static struct cftype kmem_cgroup_files[] = {
> +	{
> +		.name = "kmem.limit_in_bytes",
> +		.private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
> +		.write_string = mem_cgroup_write,
> +		.read = mem_cgroup_read,
> +	},
> +	{
> +		.name = "kmem.usage_in_bytes",
> +		.private = MEMFILE_PRIVATE(_KMEM, RES_USAGE),
> +		.read = mem_cgroup_read,
> +	},
> +	{
> +		.name = "kmem.failcnt",
> +		.private = MEMFILE_PRIVATE(_KMEM, RES_FAILCNT),
> +		.trigger = mem_cgroup_reset,
> +		.read = mem_cgroup_read,
> +	},
> +	{
> +		.name = "kmem.max_usage_in_bytes",
> +		.private = MEMFILE_PRIVATE(_KMEM, RES_MAX_USAGE),
> +		.trigger = mem_cgroup_reset,
> +		.read = mem_cgroup_read,
> +	},
> +	{},
> +};
> +
>  static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
>  {
>  	return mem_cgroup_sockets_init(memcg, ss);
> @@ -4961,6 +5015,12 @@ mem_cgroup_create(struct cgroup *cont)
>  		int cpu;
>  		enable_swap_cgroup();
>  		parent = NULL;
> +
> +#ifdef CONFIG_MEMCG_KMEM
> +		WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys,
> +					   kmem_cgroup_files));
> +#endif
> +

Why not just make it part of mem_cgroup_files[]?

Thanks.

-- 
tejun

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

>> +
>> +#ifdef CONFIG_MEMCG_KMEM
>> +		WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys,
>> +					   kmem_cgroup_files));
>> +#endif
>> +
> 
> Why not just make it part of mem_cgroup_files[]?
> 
> Thanks.
> 

Done.

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Michal Hocko]

On Tue 18-09-12 18:04:01, Glauber Costa wrote:
> This patch adds the basic infrastructure for the accounting of the slab
> caches. To control that, the following files are created:
> 
>  * memory.kmem.usage_in_bytes
>  * memory.kmem.limit_in_bytes
>  * memory.kmem.failcnt
>  * memory.kmem.max_usage_in_bytes
> 
> They have the same meaning of their user memory counterparts. They
> reflect the state of the "kmem" res_counter.

> The code is not enabled until a limit is set. 

"Per cgroup slab memory accounting is not enabled until a limit is set
for the group. Once the limit is set the accounting cannot be disabled
such a group."

Better?

> This can be tested by the flag "kmem_accounted".

Sounds as if it could be done from userspace (because you were talking
about an user interface) which it cannot and we do not see it in this
patch because it is not used anywhere. So please be more specific.

> This means that after the patch is applied, no behavioral changes
> exists for whoever is still using memcg to control their memory usage.
> 
> We always account to both user and kernel resource_counters. 

This is in contradiction with your claim that there is no behavioral
change for memcg users. Please clarify when we use u and when u+k
accounting.
"
There is no behavioral change if the kmem accounting is turned off for
memcg users but when there is a kmem.limit_in_bytes is set then the
memory.usage_in_bytes will include both user and kmem memory.
"

> This
> effectively means that an independent kernel limit is in place when the
> limit is set to a lower value than the user memory. A equal or higher
> value means that the user limit will always hit first, meaning that kmem
> is effectively unlimited.
> 
> People who want to track kernel memory but not limit it, can set this
> limit to a very high number (like RESOURCE_MAX - 1page - that no one
> will ever hit, or equal to the user memory)
> 
> Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
> CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
> CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
> ---
>  mm/memcontrol.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 63 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d6ad138..f3fd354 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -265,6 +265,10 @@ struct mem_cgroup {
>  	};
>  
>  	/*
> +	 * the counter to account for kernel memory usage.
> +	 */
> +	struct res_counter kmem;
> +	/*
>  	 * Per cgroup active and inactive list, similar to the
>  	 * per zone LRU lists.
>  	 */
> @@ -279,6 +283,7 @@ struct mem_cgroup {
>  	 * Should the accounting and control be hierarchical, per subtree?
>  	 */
>  	bool use_hierarchy;
> +	bool kmem_accounted;
>  
>  	bool		oom_lock;
>  	atomic_t	under_oom;
> @@ -389,6 +394,7 @@ enum res_type {
>  	_MEM,
>  	_MEMSWAP,
>  	_OOM_TYPE,
> +	_KMEM,
>  };
>  
>  #define MEMFILE_PRIVATE(x, val)	((x) << 16 | (val))
> @@ -1439,6 +1445,10 @@ done:
>  		res_counter_read_u64(&memcg->memsw, RES_USAGE) >> 10,
>  		res_counter_read_u64(&memcg->memsw, RES_LIMIT) >> 10,
>  		res_counter_read_u64(&memcg->memsw, RES_FAILCNT));
> +	printk(KERN_INFO "kmem: usage %llukB, limit %llukB, failcnt %llu\n",
> +		res_counter_read_u64(&memcg->kmem, RES_USAGE) >> 10,
> +		res_counter_read_u64(&memcg->kmem, RES_LIMIT) >> 10,
> +		res_counter_read_u64(&memcg->kmem, RES_FAILCNT));
>  }
>  
>  /*
> @@ -3946,6 +3956,9 @@ static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
>  		else
>  			val = res_counter_read_u64(&memcg->memsw, name);
>  		break;
> +	case _KMEM:
> +		val = res_counter_read_u64(&memcg->kmem, name);
> +		break;
>  	default:
>  		BUG();
>  	}
> @@ -3984,8 +3997,18 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
>  			break;
>  		if (type == _MEM)
>  			ret = mem_cgroup_resize_limit(memcg, val);
> -		else
> +		else if (type == _MEMSWAP)
>  			ret = mem_cgroup_resize_memsw_limit(memcg, val);
> +		else if (type == _KMEM) {
> +			ret = res_counter_set_limit(&memcg->kmem, val);
> +			if (ret)
> +				break;
> +
> +			/* For simplicity, we won't allow this to be disabled */
> +			if (!memcg->kmem_accounted && val != RESOURCE_MAX)
> +				memcg->kmem_accounted = true;
> +		} else
> +			return -EINVAL;
>  		break;
>  	case RES_SOFT_LIMIT:
>  		ret = res_counter_memparse_write_strategy(buffer, &val);
> @@ -4051,12 +4074,16 @@ static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
>  	case RES_MAX_USAGE:
>  		if (type == _MEM)
>  			res_counter_reset_max(&memcg->res);
> +		else if (type == _KMEM)
> +			res_counter_reset_max(&memcg->kmem);
>  		else
>  			res_counter_reset_max(&memcg->memsw);
>  		break;
>  	case RES_FAILCNT:
>  		if (type == _MEM)
>  			res_counter_reset_failcnt(&memcg->res);
> +		else if (type == _KMEM)
> +			res_counter_reset_failcnt(&memcg->kmem);
>  		else
>  			res_counter_reset_failcnt(&memcg->memsw);
>  		break;
> @@ -4618,6 +4645,33 @@ static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
>  }
>  
>  #ifdef CONFIG_MEMCG_KMEM

Some things are guarded CONFIG_MEMCG_KMEM but some are not (e.g. struct
mem_cgroup.kmem). I do understand you want to keep ifdefs on the leash
but we should clean this up one day.

> +static struct cftype kmem_cgroup_files[] = {
> +	{
> +		.name = "kmem.limit_in_bytes",
> +		.private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
> +		.write_string = mem_cgroup_write,
> +		.read = mem_cgroup_read,
> +	},
> +	{
> +		.name = "kmem.usage_in_bytes",
> +		.private = MEMFILE_PRIVATE(_KMEM, RES_USAGE),
> +		.read = mem_cgroup_read,
> +	},
> +	{
> +		.name = "kmem.failcnt",
> +		.private = MEMFILE_PRIVATE(_KMEM, RES_FAILCNT),
> +		.trigger = mem_cgroup_reset,
> +		.read = mem_cgroup_read,
> +	},
> +	{
> +		.name = "kmem.max_usage_in_bytes",
> +		.private = MEMFILE_PRIVATE(_KMEM, RES_MAX_USAGE),
> +		.trigger = mem_cgroup_reset,
> +		.read = mem_cgroup_read,
> +	},
> +	{},
> +};
> +
>  static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
>  {
>  	return mem_cgroup_sockets_init(memcg, ss);
> @@ -4961,6 +5015,12 @@ mem_cgroup_create(struct cgroup *cont)
>  		int cpu;
>  		enable_swap_cgroup();
>  		parent = NULL;
> +
> +#ifdef CONFIG_MEMCG_KMEM
> +		WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys,
> +					   kmem_cgroup_files));
> +#endif
> +
>  		if (mem_cgroup_soft_limit_tree_init())
>  			goto free_out;
>  		root_mem_cgroup = memcg;
> @@ -4979,6 +5039,7 @@ mem_cgroup_create(struct cgroup *cont)
>  	if (parent && parent->use_hierarchy) {
>  		res_counter_init(&memcg->res, &parent->res);
>  		res_counter_init(&memcg->memsw, &parent->memsw);
> +		res_counter_init(&memcg->kmem, &parent->kmem);

Haven't we already discussed that a new memcg should inherit kmem_accounted
from its parent for use_hierarchy?
Say we have
root
|
A (kmem_accounted = 1, use_hierachy = 1)
 \
  B (kmem_accounted = 0)
   \
    C (kmem_accounted = 1)

B find's itself in an awkward situation becuase it doesn't want to
account u+k but it ends up doing so becuase C.
-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/26/2012 06:03 PM, Michal Hocko wrote:
> On Tue 18-09-12 18:04:01, Glauber Costa wrote:
>> This patch adds the basic infrastructure for the accounting of the slab
>> caches. To control that, the following files are created:
>>
>>  * memory.kmem.usage_in_bytes
>>  * memory.kmem.limit_in_bytes
>>  * memory.kmem.failcnt
>>  * memory.kmem.max_usage_in_bytes
>>
>> They have the same meaning of their user memory counterparts. They
>> reflect the state of the "kmem" res_counter.
> 
>> The code is not enabled until a limit is set. 
> 
> "Per cgroup slab memory accounting is not enabled until a limit is set
> for the group. Once the limit is set the accounting cannot be disabled
> such a group."
> 
> Better?
> 
>> This can be tested by the flag "kmem_accounted".
> 
> Sounds as if it could be done from userspace (because you were talking
> about an user interface) which it cannot and we do not see it in this
> patch because it is not used anywhere. So please be more specific.
> 
>> This means that after the patch is applied, no behavioral changes
>> exists for whoever is still using memcg to control their memory usage.
>>
>> We always account to both user and kernel resource_counters. 
> 
> This is in contradiction with your claim that there is no behavioral
> change for memcg users. Please clarify when we use u and when u+k
> accounting.
> "
> There is no behavioral change if the kmem accounting is turned off for
> memcg users but when there is a kmem.limit_in_bytes is set then the
> memory.usage_in_bytes will include both user and kmem memory.
> "
> 
>> This
>> effectively means that an independent kernel limit is in place when the
>> limit is set to a lower value than the user memory. A equal or higher
>> value means that the user limit will always hit first, meaning that kmem
>> is effectively unlimited.
>>
>> People who want to track kernel memory but not limit it, can set this
>> limit to a very high number (like RESOURCE_MAX - 1page - that no one
>> will ever hit, or equal to the user memory)
>>
>> Signed-off-by: Glauber Costa <glommer@parallels.com>
>> CC: Michal Hocko <mhocko@suse.cz>
>> CC: Johannes Weiner <hannes@cmpxchg.org>
>> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>> ---
>>  mm/memcontrol.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 63 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index d6ad138..f3fd354 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -265,6 +265,10 @@ struct mem_cgroup {
>>  	};
>>  
>>  	/*
>> +	 * the counter to account for kernel memory usage.
>> +	 */
>> +	struct res_counter kmem;
>> +	/*
>>  	 * Per cgroup active and inactive list, similar to the
>>  	 * per zone LRU lists.
>>  	 */
>> @@ -279,6 +283,7 @@ struct mem_cgroup {
>>  	 * Should the accounting and control be hierarchical, per subtree?
>>  	 */
>>  	bool use_hierarchy;
>> +	bool kmem_accounted;
>>  
>>  	bool		oom_lock;
>>  	atomic_t	under_oom;
>> @@ -389,6 +394,7 @@ enum res_type {
>>  	_MEM,
>>  	_MEMSWAP,
>>  	_OOM_TYPE,
>> +	_KMEM,
>>  };
>>  
>>  #define MEMFILE_PRIVATE(x, val)	((x) << 16 | (val))
>> @@ -1439,6 +1445,10 @@ done:
>>  		res_counter_read_u64(&memcg->memsw, RES_USAGE) >> 10,
>>  		res_counter_read_u64(&memcg->memsw, RES_LIMIT) >> 10,
>>  		res_counter_read_u64(&memcg->memsw, RES_FAILCNT));
>> +	printk(KERN_INFO "kmem: usage %llukB, limit %llukB, failcnt %llu\n",
>> +		res_counter_read_u64(&memcg->kmem, RES_USAGE) >> 10,
>> +		res_counter_read_u64(&memcg->kmem, RES_LIMIT) >> 10,
>> +		res_counter_read_u64(&memcg->kmem, RES_FAILCNT));
>>  }
>>  
>>  /*
>> @@ -3946,6 +3956,9 @@ static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
>>  		else
>>  			val = res_counter_read_u64(&memcg->memsw, name);
>>  		break;
>> +	case _KMEM:
>> +		val = res_counter_read_u64(&memcg->kmem, name);
>> +		break;
>>  	default:
>>  		BUG();
>>  	}
>> @@ -3984,8 +3997,18 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
>>  			break;
>>  		if (type == _MEM)
>>  			ret = mem_cgroup_resize_limit(memcg, val);
>> -		else
>> +		else if (type == _MEMSWAP)
>>  			ret = mem_cgroup_resize_memsw_limit(memcg, val);
>> +		else if (type == _KMEM) {
>> +			ret = res_counter_set_limit(&memcg->kmem, val);
>> +			if (ret)
>> +				break;
>> +
>> +			/* For simplicity, we won't allow this to be disabled */
>> +			if (!memcg->kmem_accounted && val != RESOURCE_MAX)
>> +				memcg->kmem_accounted = true;
>> +		} else
>> +			return -EINVAL;
>>  		break;
>>  	case RES_SOFT_LIMIT:
>>  		ret = res_counter_memparse_write_strategy(buffer, &val);
>> @@ -4051,12 +4074,16 @@ static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
>>  	case RES_MAX_USAGE:
>>  		if (type == _MEM)
>>  			res_counter_reset_max(&memcg->res);
>> +		else if (type == _KMEM)
>> +			res_counter_reset_max(&memcg->kmem);
>>  		else
>>  			res_counter_reset_max(&memcg->memsw);
>>  		break;
>>  	case RES_FAILCNT:
>>  		if (type == _MEM)
>>  			res_counter_reset_failcnt(&memcg->res);
>> +		else if (type == _KMEM)
>> +			res_counter_reset_failcnt(&memcg->kmem);
>>  		else
>>  			res_counter_reset_failcnt(&memcg->memsw);
>>  		break;
>> @@ -4618,6 +4645,33 @@ static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
>>  }
>>  
>>  #ifdef CONFIG_MEMCG_KMEM
> 
> Some things are guarded CONFIG_MEMCG_KMEM but some are not (e.g. struct
> mem_cgroup.kmem). I do understand you want to keep ifdefs on the leash
> but we should clean this up one day.
> 
>> +static struct cftype kmem_cgroup_files[] = {
>> +	{
>> +		.name = "kmem.limit_in_bytes",
>> +		.private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
>> +		.write_string = mem_cgroup_write,
>> +		.read = mem_cgroup_read,
>> +	},
>> +	{
>> +		.name = "kmem.usage_in_bytes",
>> +		.private = MEMFILE_PRIVATE(_KMEM, RES_USAGE),
>> +		.read = mem_cgroup_read,
>> +	},
>> +	{
>> +		.name = "kmem.failcnt",
>> +		.private = MEMFILE_PRIVATE(_KMEM, RES_FAILCNT),
>> +		.trigger = mem_cgroup_reset,
>> +		.read = mem_cgroup_read,
>> +	},
>> +	{
>> +		.name = "kmem.max_usage_in_bytes",
>> +		.private = MEMFILE_PRIVATE(_KMEM, RES_MAX_USAGE),
>> +		.trigger = mem_cgroup_reset,
>> +		.read = mem_cgroup_read,
>> +	},
>> +	{},
>> +};
>> +
>>  static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
>>  {
>>  	return mem_cgroup_sockets_init(memcg, ss);
>> @@ -4961,6 +5015,12 @@ mem_cgroup_create(struct cgroup *cont)
>>  		int cpu;
>>  		enable_swap_cgroup();
>>  		parent = NULL;
>> +
>> +#ifdef CONFIG_MEMCG_KMEM
>> +		WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys,
>> +					   kmem_cgroup_files));
>> +#endif
>> +
>>  		if (mem_cgroup_soft_limit_tree_init())
>>  			goto free_out;
>>  		root_mem_cgroup = memcg;
>> @@ -4979,6 +5039,7 @@ mem_cgroup_create(struct cgroup *cont)
>>  	if (parent && parent->use_hierarchy) {
>>  		res_counter_init(&memcg->res, &parent->res);
>>  		res_counter_init(&memcg->memsw, &parent->memsw);
>> +		res_counter_init(&memcg->kmem, &parent->kmem);
> 
> Haven't we already discussed that a new memcg should inherit kmem_accounted
> from its parent for use_hierarchy?
> Say we have
> root
> |
> A (kmem_accounted = 1, use_hierachy = 1)
>  \
>   B (kmem_accounted = 0)
>    \
>     C (kmem_accounted = 1)
> 
> B find's itself in an awkward situation becuase it doesn't want to
> account u+k but it ends up doing so becuase C.
> 

Ok, I haven't updated it here. But that should be taken care of in the
lifecycle patch.

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Michal Hocko]

On Wed 26-09-12 18:33:10, Glauber Costa wrote:
> On 09/26/2012 06:03 PM, Michal Hocko wrote:
> > On Tue 18-09-12 18:04:01, Glauber Costa wrote:
[...]
> >> @@ -4961,6 +5015,12 @@ mem_cgroup_create(struct cgroup *cont)
> >>  		int cpu;
> >>  		enable_swap_cgroup();
> >>  		parent = NULL;
> >> +
> >> +#ifdef CONFIG_MEMCG_KMEM
> >> +		WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys,
> >> +					   kmem_cgroup_files));
> >> +#endif
> >> +
> >>  		if (mem_cgroup_soft_limit_tree_init())
> >>  			goto free_out;
> >>  		root_mem_cgroup = memcg;
> >> @@ -4979,6 +5039,7 @@ mem_cgroup_create(struct cgroup *cont)
> >>  	if (parent && parent->use_hierarchy) {
> >>  		res_counter_init(&memcg->res, &parent->res);
> >>  		res_counter_init(&memcg->memsw, &parent->memsw);
> >> +		res_counter_init(&memcg->kmem, &parent->kmem);
> > 
> > Haven't we already discussed that a new memcg should inherit kmem_accounted
> > from its parent for use_hierarchy?
> > Say we have
> > root
> > |
> > A (kmem_accounted = 1, use_hierachy = 1)
> >  \
> >   B (kmem_accounted = 0)
> >    \
> >     C (kmem_accounted = 1)
> > 
> > B find's itself in an awkward situation becuase it doesn't want to
> > account u+k but it ends up doing so becuase C.
> > 
> 
> Ok, I haven't updated it here. But that should be taken care of in the
> lifecycle patch.

I am not sure which patch you are thinking about but I would prefer to
have it here because it is safe wrt. races and it is more obvious as
well.

-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/26/2012 08:01 PM, Michal Hocko wrote:
> On Wed 26-09-12 18:33:10, Glauber Costa wrote:
>> On 09/26/2012 06:03 PM, Michal Hocko wrote:
>>> On Tue 18-09-12 18:04:01, Glauber Costa wrote:
> [...]
>>>> @@ -4961,6 +5015,12 @@ mem_cgroup_create(struct cgroup *cont)
>>>>  		int cpu;
>>>>  		enable_swap_cgroup();
>>>>  		parent = NULL;
>>>> +
>>>> +#ifdef CONFIG_MEMCG_KMEM
>>>> +		WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys,
>>>> +					   kmem_cgroup_files));
>>>> +#endif
>>>> +
>>>>  		if (mem_cgroup_soft_limit_tree_init())
>>>>  			goto free_out;
>>>>  		root_mem_cgroup = memcg;
>>>> @@ -4979,6 +5039,7 @@ mem_cgroup_create(struct cgroup *cont)
>>>>  	if (parent && parent->use_hierarchy) {
>>>>  		res_counter_init(&memcg->res, &parent->res);
>>>>  		res_counter_init(&memcg->memsw, &parent->memsw);
>>>> +		res_counter_init(&memcg->kmem, &parent->kmem);
>>>
>>> Haven't we already discussed that a new memcg should inherit kmem_accounted
>>> from its parent for use_hierarchy?
>>> Say we have
>>> root
>>> |
>>> A (kmem_accounted = 1, use_hierachy = 1)
>>>  \
>>>   B (kmem_accounted = 0)
>>>    \
>>>     C (kmem_accounted = 1)
>>>
>>> B find's itself in an awkward situation becuase it doesn't want to
>>> account u+k but it ends up doing so becuase C.
>>>
>>
>> Ok, I haven't updated it here. But that should be taken care of in the
>> lifecycle patch.
> 
> I am not sure which patch you are thinking about but I would prefer to
> have it here because it is safe wrt. races and it is more obvious as
> well.
> 

The patch where I make kmem_accounted into a bitfield. So any code here
will eventually disappear.

But BTW, I am not saying I won't update the patch - I like that all
patches work and make sense in their own, I am just saying that I forgot
to update this patch, because I added the code in its final version to
the end and then squashed it.


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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Michal, Glauber.

On Wed, Sep 26, 2012 at 04:03:47PM +0200, Michal Hocko wrote:
> Haven't we already discussed that a new memcg should inherit kmem_accounted
> from its parent for use_hierarchy?
> Say we have
> root
> |
> A (kmem_accounted = 1, use_hierachy = 1)
>  \
>   B (kmem_accounted = 0)
>    \
>     C (kmem_accounted = 1)
> 
> B find's itself in an awkward situation becuase it doesn't want to
> account u+k but it ends up doing so becuase C.

Do we really want this level of flexibility?  What's wrong with a
global switch at the root?  I'm not even sure we want this to be
optional at all.  The only reason I can think of is that it might
screw up some configurations in use which are carefully crafted to
suit userland-only usage but for that isn't what we need a transition
plan rather than another ultra flexible config option that not many
really understand the implication of?

In the same vein, do we really need both .kmem_accounted and config
option?  If someone is turning on MEMCG, just include kmem accounting.

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/26/2012 08:36 PM, Tejun Heo wrote:
> Hello, Michal, Glauber.
> 
> On Wed, Sep 26, 2012 at 04:03:47PM +0200, Michal Hocko wrote:
>> Haven't we already discussed that a new memcg should inherit kmem_accounted
>> from its parent for use_hierarchy?
>> Say we have
>> root
>> |
>> A (kmem_accounted = 1, use_hierachy = 1)
>>  \
>>   B (kmem_accounted = 0)
>>    \
>>     C (kmem_accounted = 1)
>>
>> B find's itself in an awkward situation becuase it doesn't want to
>> account u+k but it ends up doing so becuase C.
> 
> Do we really want this level of flexibility?  What's wrong with a
> global switch at the root?  I'm not even sure we want this to be
> optional at all.  The only reason I can think of is that it might
> screw up some configurations in use which are carefully crafted to
> suit userland-only usage but for that isn't what we need a transition
> plan rather than another ultra flexible config option that not many
> really understand the implication of?
> 
> In the same vein, do we really need both .kmem_accounted and config
> option?  If someone is turning on MEMCG, just include kmem accounting.
> 

Yes, we do.

This was discussed multiple times. Our interest is to preserve existing
deployed setup, that were tuned in a world where kmem didn't exist.
Because we also feed kmem to the user counter, this may very well
disrupt their setup.

User memory, unlike kernel memory, may very well be totally in control
of the userspace application, so it is not unreasonable to believe that
extra pages appearing in a new kernel version may break them.

It is actually a much worse compatibility problem than flipping
hierarchy, in comparison

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Glauber.

On Wed, Sep 26, 2012 at 10:36 AM, Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org> wrote:
> This was discussed multiple times. Our interest is to preserve existing
> deployed setup, that were tuned in a world where kmem didn't exist.
> Because we also feed kmem to the user counter, this may very well
> disrupt their setup.

So, that can be served by .kmem_accounted at root, no?

> User memory, unlike kernel memory, may very well be totally in control
> of the userspace application, so it is not unreasonable to believe that
> extra pages appearing in a new kernel version may break them.
>
> It is actually a much worse compatibility problem than flipping
> hierarchy, in comparison

Again, what's wrong with one switch at the root?

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/26/2012 09:44 PM, Tejun Heo wrote:
> Hello, Glauber.
> 
> On Wed, Sep 26, 2012 at 10:36 AM, Glauber Costa <glommer@parallels.com> wrote:
>> This was discussed multiple times. Our interest is to preserve existing
>> deployed setup, that were tuned in a world where kmem didn't exist.
>> Because we also feed kmem to the user counter, this may very well
>> disrupt their setup.
> 
> So, that can be served by .kmem_accounted at root, no?
> 
>> User memory, unlike kernel memory, may very well be totally in control
>> of the userspace application, so it is not unreasonable to believe that
>> extra pages appearing in a new kernel version may break them.
>>
>> It is actually a much worse compatibility problem than flipping
>> hierarchy, in comparison
> 
> Again, what's wrong with one switch at the root?
> 

I understand your trauma about over flexibility, and you know I share of
it. But I don't think there is any need to cap it here. Given kmem
accounted is perfectly hierarchical, and there seem to be plenty of
people who only care about user memory, I see no reason to disallow a
mixed use case here.

I must say that for my particular use case, enabling it unconditionally
would just work, so it is not that what I have in mind.

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello,

On Wed, Sep 26, 2012 at 09:53:09PM +0400, Glauber Costa wrote:
> I understand your trauma about over flexibility, and you know I share of
> it. But I don't think there is any need to cap it here. Given kmem
> accounted is perfectly hierarchical, and there seem to be plenty of
> people who only care about user memory, I see no reason to disallow a
> mixed use case here.
> 
> I must say that for my particular use case, enabling it unconditionally
> would just work, so it is not that what I have in mind.

So, I'm not gonna go as far as pushing for enabling it unconditionally
but would really like to hear why it's necessary to make it per node
instead of one global switch.  Maybe it has already been discussed to
hell and back.  Care to summarize / point me to it?

Thanks.

-- 
tejun

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/26/2012 10:01 PM, Tejun Heo wrote:
> Hello,
> 
> On Wed, Sep 26, 2012 at 09:53:09PM +0400, Glauber Costa wrote:
>> I understand your trauma about over flexibility, and you know I share of
>> it. But I don't think there is any need to cap it here. Given kmem
>> accounted is perfectly hierarchical, and there seem to be plenty of
>> people who only care about user memory, I see no reason to disallow a
>> mixed use case here.
>>
>> I must say that for my particular use case, enabling it unconditionally
>> would just work, so it is not that what I have in mind.
> 
> So, I'm not gonna go as far as pushing for enabling it unconditionally
> but would really like to hear why it's necessary to make it per node
> instead of one global switch.  Maybe it has already been discussed to
> hell and back.  Care to summarize / point me to it?
> 

For me, it is the other way around: it makes perfect sense to have a
per-subtree selection of features where it doesn't hurt us, provided it
is hierarchical. For the mere fact that not every application is
interested in this (Michal is the one that is being so far more vocal
about this not being needed in some use cases), and it is perfectly
valid to imagine such applications would coexist.

So given the flexibility it brings, the real question is, as I said,
backwards: what is it necessary to make it a global switch ?

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello,

On Wed, Sep 26, 2012 at 10:56:09PM +0400, Glauber Costa wrote:
> For me, it is the other way around: it makes perfect sense to have a
> per-subtree selection of features where it doesn't hurt us, provided it
> is hierarchical. For the mere fact that not every application is
> interested in this (Michal is the one that is being so far more vocal
> about this not being needed in some use cases), and it is perfectly
> valid to imagine such applications would coexist.
> 
> So given the flexibility it brings, the real question is, as I said,
> backwards: what is it necessary to make it a global switch ?

Because it hurts my head and it's better to keep things simple.  We're
planning to retire .use_hierarhcy in sub hierarchies and I'd really
like to prevent another fiasco like that unless there absolutely is no
way around it.  Flexibility where necessary is fine but let's please
try our best to avoid over-designing things.  We've been far too good
at getting lost in flexbility maze.  Michal, care to chime in?

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/26/2012 11:34 PM, Tejun Heo wrote:
> Hello,
> 
> On Wed, Sep 26, 2012 at 10:56:09PM +0400, Glauber Costa wrote:
>> For me, it is the other way around: it makes perfect sense to have a
>> per-subtree selection of features where it doesn't hurt us, provided it
>> is hierarchical. For the mere fact that not every application is
>> interested in this (Michal is the one that is being so far more vocal
>> about this not being needed in some use cases), and it is perfectly
>> valid to imagine such applications would coexist.
>>
>> So given the flexibility it brings, the real question is, as I said,
>> backwards: what is it necessary to make it a global switch ?
> 
> Because it hurts my head and it's better to keep things simple.  We're
> planning to retire .use_hierarhcy in sub hierarchies and I'd really
> like to prevent another fiasco like that unless there absolutely is no
> way around it.  Flexibility where necessary is fine but let's please
> try our best to avoid over-designing things.  We've been far too good
> at getting lost in flexbility maze.  Michal, care to chime in?
> 

I would very much like to hear Michal here as well, sure.

But as I said in this very beginning of this, you pretty much know that
I am heavily involved in trying to get rid of use_hierarchy, and by no
means I consider this en pair with that.

use_hierarchy is a hack around a core property of cgroups, the fact that
they are hierarchical. Its mere existence came to be to overcome a
performance limitation.

It puts you in contradictory situation where you have cgroups organized
as directories, and then not satisfied in making this hierarchical
representation be gravely ignored, forces you to use nonsensical terms
like "flat hierarchy", making us grasp at how it is to be a politician
once in our lifetimes.

Besides not being part of cgroup core, and respecting very much both
cgroups' and basic sanity properties, kmem is an actual feature that
some people want, and some people don't. There is no reason to believe
that applications that want will live in the same environment with ones
that don't want.



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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello,

On Wed, Sep 26, 2012 at 11:46:37PM +0400, Glauber Costa wrote:
> Besides not being part of cgroup core, and respecting very much both
> cgroups' and basic sanity properties, kmem is an actual feature that
> some people want, and some people don't. There is no reason to believe
> that applications that want will live in the same environment with ones
> that don't want.

I don't know.  It definitely is less crazy than .use_hierarchy but I
wouldn't say it's an inherently different thing.  I mean, what does it
even mean to have u+k limit on one subtree and not on another branch?
And we worry about things like what if parent doesn't enable it but
its chlidren do.

This is a feature which adds complexity.  If the feature is necessary
and justified, sure.  If not, let's please not and let's err on the
side of conservativeness.  We can always add it later but the other
direction is much harder.

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/26/2012 11:56 PM, Tejun Heo wrote:
> Hello,
> 
> On Wed, Sep 26, 2012 at 11:46:37PM +0400, Glauber Costa wrote:
>> Besides not being part of cgroup core, and respecting very much both
>> cgroups' and basic sanity properties, kmem is an actual feature that
>> some people want, and some people don't. There is no reason to believe
>> that applications that want will live in the same environment with ones
>> that don't want.
> 
> I don't know.  It definitely is less crazy than .use_hierarchy but I
> wouldn't say it's an inherently different thing.  I mean, what does it
> even mean to have u+k limit on one subtree and not on another branch?
> And we worry about things like what if parent doesn't enable it but
> its chlidren do.
> 

It is inherently different. To begin with, it actually contemplates two
use cases. It is not a work around.

The meaning is also very well defined. The meaning of having this
enabled in one subtree and not in other is: Subtree A wants to track
kernel memory. Subtree B does not. It's that, and never more than that.
There is no maybes and no buts, no magic knobs that makes it behave in a
crazy way.

If a children enables it but the parent does not, this does what every
tree does: enable it from that point downwards.

> This is a feature which adds complexity.  If the feature is necessary
> and justified, sure.  If not, let's please not and let's err on the
> side of conservativeness.  We can always add it later but the other
> direction is much harder.
> 

I disagree. Having kmem tracking adds complexity. Having to cope with
the use case where we turn it on dynamically to cope with the "user page
only" use case adds complexity. But I see no significant complexity
being added by having it per subtree. Really.

You have the use_hierarchy fiasco in mind, and I do understand that you
are raising the flag and all that.

But think in terms of functionality: This thing here is a lot more
similar to swap than use_hierarchy. Would you argue that memsw should be
per-root ?

The reason why it shouldn't: Some people want to limit memory
consumption all the way to the swap, some people don't. Same with kmem.


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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

On Thu, Sep 27, 2012 at 12:02:14AM +0400, Glauber Costa wrote:
> But think in terms of functionality: This thing here is a lot more
> similar to swap than use_hierarchy. Would you argue that memsw should be
> per-root ?

I'm fairly sure you can make about the same argument about
use_hierarchy.  There is a choice to make here and one is simpler than
the other.  I want the additional complexity justified by actual use
cases which isn't too much to ask for especially when the complexity
is something visible to userland.

So let's please stop arguing semantics.  If this is definitely
necessary for some use cases, sure let's have it.  If not, let's
consider it later.  I'll stop responding on "inherent differences."  I
don't think we'll get anywhere with that.

Michal, Johannes, Kamezawa, what are your thoughts?

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/27/2012 12:16 AM, Tejun Heo wrote:
> On Thu, Sep 27, 2012 at 12:02:14AM +0400, Glauber Costa wrote:
>> But think in terms of functionality: This thing here is a lot more
>> similar to swap than use_hierarchy. Would you argue that memsw should be
>> per-root ?
> 
> I'm fairly sure you can make about the same argument about
> use_hierarchy.  There is a choice to make here and one is simpler than
> the other.  I want the additional complexity justified by actual use
> cases which isn't too much to ask for especially when the complexity
> is something visible to userland.
> 
> So let's please stop arguing semantics.  If this is definitely
> necessary for some use cases, sure let's have it.  If not, let's
> consider it later.  I'll stop responding on "inherent differences."  I
> don't think we'll get anywhere with that.
> 

If you stop responding, we are for sure not getting anywhere. I agree
with you here.

Let me point out one issue that you seem to be missing, and you respond
or not, your call.

"kmem_accounted" is not a switch. It is an internal representation only.
The semantics, that we discussed exhaustively in San Diego, is that a
group that is not limited is not accounted. This is simple and consistent.

Since the limits are still per-cgroup, you are actually proposing more
user-visible complexity than me, since you are adding yet another file,
with its own semantics.

About use cases, I've already responded: my containers use case is kmem
limited. There are people like Michal that specifically asked for
user-only semantics to be preserved. So your question for global vs
local switch (that again, doesn't exist; only a local *limit* exists)
should really be posed in the following way:
"Can two different use cases with different needs be hosted in the same
box?"



> Michal, Johannes, Kamezawa, what are your thoughts?
>
waiting! =)

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Glauber.

On Thu, Sep 27, 2012 at 01:24:40AM +0400, Glauber Costa wrote:
> "kmem_accounted" is not a switch. It is an internal representation only.
> The semantics, that we discussed exhaustively in San Diego, is that a
> group that is not limited is not accounted. This is simple and consistent.
> 
> Since the limits are still per-cgroup, you are actually proposing more
> user-visible complexity than me, since you are adding yet another file,
> with its own semantics.

I was confused.  I thought it was exposed as a switch to userland (it
being right below .use_hierarchy tripped red alert).  This is internal
flag dependent upon kernel limit being set.  My apologies.

So, the proposed behavior is to allow enabling kmemcg anytime but
ignore what happened inbetween?  Where the knob is changes but the
weirdity seems all the same.  What prevents us from having a single
switch at root which can only be flipped when there's no children?

Backward compatibility is covered with single switch and I really
don't think "you can enable limits for kernel memory anytime but we
don't keep track of whatever happened before it was flipped the first
time because the first time is always special" is a sane thing to
expose to userland.  Or am I misunderstanding the proposed behavior
again?

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/27/2012 02:10 AM, Tejun Heo wrote:
> Hello, Glauber.
> 
> On Thu, Sep 27, 2012 at 01:24:40AM +0400, Glauber Costa wrote:
>> "kmem_accounted" is not a switch. It is an internal representation only.
>> The semantics, that we discussed exhaustively in San Diego, is that a
>> group that is not limited is not accounted. This is simple and consistent.
>>
>> Since the limits are still per-cgroup, you are actually proposing more
>> user-visible complexity than me, since you are adding yet another file,
>> with its own semantics.
> 
> I was confused.  I thought it was exposed as a switch to userland (it
> being right below .use_hierarchy tripped red alert). 

Remember I was the one more vocally and radically so far trying to get
rid of use_hierarchy. I should have been more clear - and I was, as soon
as I better understood the nature of your opposition - but this is
precisely what I meant by "inherently different".

> 
> So, the proposed behavior is to allow enabling kmemcg anytime but
> ignore what happened inbetween?  Where the knob is changes but the
> weirdity seems all the same.  What prevents us from having a single
> switch at root which can only be flipped when there's no children?

So I view this very differently from you. We have no root-only switches
in memcg. This would be a first, and this is the kind of thing that adds
complexity, in my view.

You have someone like libvirt or a systemd service using memcg. It
probably starts at boot. Once it is started, it will pretty much prevent
switching of any global switch like this.

And then what? If you want a different behavior you need to go kill all
your services that are using memcg so you can get the behavior you want?
And if they happen to be making a specific flag choice by design, you
just say "you really can't run A + B together" ?

I myself think global switches are an unnecessary complication. And let
us not talk about use_hierarchy, please. If it becomes global, it is
going to be as part of a phase out plan anyway. The problem with that is
not that it is global, is that it shouldn't even exist.

> 
> Backward compatibility is covered with single switch and I really
> don't think "you can enable limits for kernel memory anytime but we
> don't keep track of whatever happened before it was flipped the first
> time because the first time is always special" is a sane thing to
> expose to userland.  Or am I misunderstanding the proposed behavior
> again?
> 

You do keep track. Before you switch it for the first time, it all
belongs to the root memcg.

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Glauber.

On Thu, Sep 27, 2012 at 02:29:06AM +0400, Glauber Costa wrote:
> And then what? If you want a different behavior you need to go kill all
> your services that are using memcg so you can get the behavior you want?
> And if they happen to be making a specific flag choice by design, you
> just say "you really can't run A + B together" ?
> 
> I myself think global switches are an unnecessary complication. And let
> us not talk about use_hierarchy, please. If it becomes global, it is
> going to be as part of a phase out plan anyway. The problem with that is
> not that it is global, is that it shouldn't even exist.

I would consider it more of a compatibility thing which is set during
boot and configurable by sysadmin.  Let the newer systems enable it by
default on boot and old configs / special ones disable it as
necessary.

> > Backward compatibility is covered with single switch and I really
> > don't think "you can enable limits for kernel memory anytime but we
> > don't keep track of whatever happened before it was flipped the first
> > time because the first time is always special" is a sane thing to
> > expose to userland.  Or am I misunderstanding the proposed behavior
> > again?
> 
> You do keep track. Before you switch it for the first time, it all
> belongs to the root memcg.

Well, that's really playing with words.  Limit is per cgroup and
before the limit is set for the first time, everything is accounted to
something else.  How is that keeping track?

The proposed behavior seems really crazy to me.  Do people really
think this is a good idea?

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/27/2012 02:42 AM, Tejun Heo wrote:
> Hello, Glauber.
> 
> On Thu, Sep 27, 2012 at 02:29:06AM +0400, Glauber Costa wrote:
>> And then what? If you want a different behavior you need to go kill all
>> your services that are using memcg so you can get the behavior you want?
>> And if they happen to be making a specific flag choice by design, you
>> just say "you really can't run A + B together" ?
>>
>> I myself think global switches are an unnecessary complication. And let
>> us not talk about use_hierarchy, please. If it becomes global, it is
>> going to be as part of a phase out plan anyway. The problem with that is
>> not that it is global, is that it shouldn't even exist.
> 
> I would consider it more of a compatibility thing which is set during
> boot and configurable by sysadmin.  Let the newer systems enable it by
> default on boot and old configs / special ones disable it as
> necessary.
> 

I don't. Much has been said in the past about the problem of sharing. A
lot of the kernel objects are shared by nature, this is pretty much
unavoidable. The answer we have been giving to this inquiry, is that the
workloads (us) interested in kmem accounted tend to be quite local in
their file accesses (and other kernel objects as well).

It should be obvious that not all workloads are like this, and some of
them would actually prefer to have their umem limited only.

There is nothing unreasonable in tracking user memory only.

If we have a global switch for "tracking all kernel memory", who would
you account the objects that are heavily shared to? I solve this by not
tracking kernel memory for cgroups in such workloads. What do you propose?

>>> Backward compatibility is covered with single switch and I really
>>> don't think "you can enable limits for kernel memory anytime but we
>>> don't keep track of whatever happened before it was flipped the first
>>> time because the first time is always special" is a sane thing to
>>> expose to userland.  Or am I misunderstanding the proposed behavior
>>> again?
>>
>> You do keep track. Before you switch it for the first time, it all
>> belongs to the root memcg.
> 
> Well, that's really playing with words.  Limit is per cgroup and
> before the limit is set for the first time, everything is accounted to
> something else.  How is that keeping track?
> 

Even after the limit is set, it is set only by workloads that want kmem
to be tracked. If you want to track it during the whole lifetime of the
cgroup, you switch it before you put tasks to it. What is so crazy about it?

> The proposed behavior seems really crazy to me.  Do people really
> think this is a good idea?
> 

It is really sad that you lost the opportunity to say that in a room
full of mm developers that could add to this discussion in real time,
when after an explanation about this was given, Mel asked if anyone
would have any objections to this.

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Glauber.

On Thu, Sep 27, 2012 at 02:54:11AM +0400, Glauber Costa wrote:
> I don't. Much has been said in the past about the problem of sharing. A
> lot of the kernel objects are shared by nature, this is pretty much
> unavoidable. The answer we have been giving to this inquiry, is that the
> workloads (us) interested in kmem accounted tend to be quite local in
> their file accesses (and other kernel objects as well).
> 
> It should be obvious that not all workloads are like this, and some of
> them would actually prefer to have their umem limited only.
> 
> There is nothing unreasonable in tracking user memory only.
> 
> If we have a global switch for "tracking all kernel memory", who would
> you account the objects that are heavily shared to? I solve this by not
> tracking kernel memory for cgroups in such workloads. What do you propose?

One of the things wrong with that is that it exposes the limitation of
the current implementation as interface to userland, which is never a
good idea.  In addition, how is userland supposed to know which
workload is shared kmem heavy or not?  Details like that are not even
inherent to workloads.  It's highly dependent on kernel implementation
which may change any day.  If we hit workloads like that the right
thing to do is improving kmemcg so that such problems don't occur, not
exposing another switch.

If we can't make that work in reasonable (doesn't have to be perfect)
way, we might as well just give up on kmem controller.  If userland
has to second-guess kernel implementation details to make use of it,
it's useless.

> > Well, that's really playing with words.  Limit is per cgroup and
> > before the limit is set for the first time, everything is accounted to
> > something else.  How is that keeping track?
> > 
> 
> Even after the limit is set, it is set only by workloads that want kmem
> to be tracked. If you want to track it during the whole lifetime of the
> cgroup, you switch it before you put tasks to it. What is so crazy about it?

The fact that the numbers don't really mean what they apparently
should mean.

> > The proposed behavior seems really crazy to me.  Do people really
> > think this is a good idea?
> 
> It is really sad that you lost the opportunity to say that in a room
> full of mm developers that could add to this discussion in real time,
> when after an explanation about this was given, Mel asked if anyone
> would have any objections to this.

Sure, conferences are useful for building consensus but that's the
extent of it.  Sorry that I didn't realize the implications then but
conferences don't really add any finality to decisions.

So, this seems properly crazy to me at the similar level of
use_hierarchy fiasco.  I'm gonna NACK on this.

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/27/2012 03:08 AM, Tejun Heo wrote:
> Hello, Glauber.
> 
> On Thu, Sep 27, 2012 at 02:54:11AM +0400, Glauber Costa wrote:
>> I don't. Much has been said in the past about the problem of sharing. A
>> lot of the kernel objects are shared by nature, this is pretty much
>> unavoidable. The answer we have been giving to this inquiry, is that the
>> workloads (us) interested in kmem accounted tend to be quite local in
>> their file accesses (and other kernel objects as well).
>>
>> It should be obvious that not all workloads are like this, and some of
>> them would actually prefer to have their umem limited only.
>>
>> There is nothing unreasonable in tracking user memory only.
>>
>> If we have a global switch for "tracking all kernel memory", who would
>> you account the objects that are heavily shared to? I solve this by not
>> tracking kernel memory for cgroups in such workloads. What do you propose?
> 
> One of the things wrong with that is that it exposes the limitation of
> the current implementation as interface to userland, which is never a
> good idea.  In addition, how is userland supposed to know which
> workload is shared kmem heavy or not?  Details like that are not even
> inherent to workloads.  It's highly dependent on kernel implementation
> which may change any day.  If we hit workloads like that the right
> thing to do is improving kmemcg so that such problems don't occur, not
> exposing another switch.
> 

Sorry, there is nothing implementation dependent in here. One of the
biggest consumers of all this, are dentries. Dentries are related to
the paths you touch. If you touch files in a self-contained directory,
where you don't expect anyone else to touch, this can safely be
considered local. If you touch files all around, this can safely be
considered not local. Where is the implementation dependent part?

> If we can't make that work in reasonable (doesn't have to be perfect)
> way, we might as well just give up on kmem controller.  If userland
> has to second-guess kernel implementation details to make use of it,
> it's useless.
> 
As I said above, it shouldn't.

>>> Well, that's really playing with words.  Limit is per cgroup and
>>> before the limit is set for the first time, everything is accounted to
>>> something else.  How is that keeping track?
>>>
>>
>> Even after the limit is set, it is set only by workloads that want kmem
>> to be tracked. If you want to track it during the whole lifetime of the
>> cgroup, you switch it before you put tasks to it. What is so crazy about it?
> 
> The fact that the numbers don't really mean what they apparently
> should mean.
> 

This is vague. The usage file in the cgroup means how much kernel memory
was used by that cgroup. If it really bothers you that this may not be
set through the whole group's lifetime, it is also easily solvable.

> So, this seems properly crazy to me at the similar level of
> use_hierarchy fiasco.  I'm gonna NACK on this.
> 

As I said: all use cases I particularly care about are covered by a
global switch.

I am laying down my views because I really believe they make more sense.
But at some point, of course, I'll shut up if I believe I am a lone voice.

I believe it should still be good to hear from mhocko and kame, but from
your point of view, would all the rest, plus the introduction of a
global switch make it acceptable to you?

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello,

On Thu, Sep 27, 2012 at 03:20:27AM +0400, Glauber Costa wrote:
> > One of the things wrong with that is that it exposes the limitation of
> > the current implementation as interface to userland, which is never a
> > good idea.  In addition, how is userland supposed to know which
> > workload is shared kmem heavy or not?  Details like that are not even
> > inherent to workloads.  It's highly dependent on kernel implementation
> > which may change any day.  If we hit workloads like that the right
> > thing to do is improving kmemcg so that such problems don't occur, not
> > exposing another switch.
> 
> Sorry, there is nothing implementation dependent in here. One of the
> biggest consumers of all this, are dentries. Dentries are related to
> the paths you touch. If you touch files in a self-contained directory,
> where you don't expect anyone else to touch, this can safely be
> considered local. If you touch files all around, this can safely be
> considered not local. Where is the implementation dependent part?

For things like dentries and inodes and if that really matters, we
should be able to account for the usage better, no?  And frankly I'm
not even sold on that usecase.  Unless there's a way to detect and
inform about these, userland isn't gonna know that they're doing
something which consumes a lot of shared memory even that activity is
filesystem walking.  You're still asking userland to tune something
depending on parameters not easily visible from userland.  It's a lose
lose situation.

> >> Even after the limit is set, it is set only by workloads that want kmem
> >> to be tracked. If you want to track it during the whole lifetime of the
> >> cgroup, you switch it before you put tasks to it. What is so crazy about it?
> > 
> > The fact that the numbers don't really mean what they apparently
> > should mean.
> > 
> 
> This is vague. The usage file in the cgroup means how much kernel memory
> was used by that cgroup. If it really bothers you that this may not be
> set through the whole group's lifetime, it is also easily solvable.

Yes, easily by having a global switch which can be manipulated when
there's no children.  It really seems like a no brainer to me.

> > So, this seems properly crazy to me at the similar level of
> > use_hierarchy fiasco.  I'm gonna NACK on this.
> 
> As I said: all use cases I particularly care about are covered by a
> global switch.
> 
> I am laying down my views because I really believe they make more sense.
> But at some point, of course, I'll shut up if I believe I am a lone voice.
> 
> I believe it should still be good to hear from mhocko and kame, but from
> your point of view, would all the rest, plus the introduction of a
> global switch make it acceptable to you?

The only thing I'm whining about is per-node switch + silently
ignoring past accounting, so if those two are solved, I think I'm
pretty happy with the rest.

Thanks.

-- 
tejun

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Michal Hocko]

On Wed 26-09-12 16:33:34, Tejun Heo wrote:
[...]
> > > So, this seems properly crazy to me at the similar level of
> > > use_hierarchy fiasco.  I'm gonna NACK on this.
> > 
> > As I said: all use cases I particularly care about are covered by a
> > global switch.
> > 
> > I am laying down my views because I really believe they make more sense.
> > But at some point, of course, I'll shut up if I believe I am a lone voice.
> > 
> > I believe it should still be good to hear from mhocko and kame, but from
> > your point of view, would all the rest, plus the introduction of a
> > global switch make it acceptable to you?
> 
> The only thing I'm whining about is per-node switch + silently
> ignoring past accounting, so if those two are solved, I think I'm
> pretty happy with the rest.

I think that per-group "switch" is not nice as well but if we make it
hierarchy specific (which I am proposing for quite some time) and do not
let enable accounting for a group with tasks then we get both
flexibility and reasonable semantic. A global switch sounds too coars to
me and it really not necessary.

Would this work with you?
-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/27/2012 04:15 PM, Michal Hocko wrote:
> On Wed 26-09-12 16:33:34, Tejun Heo wrote:
> [...]
>>>> So, this seems properly crazy to me at the similar level of
>>>> use_hierarchy fiasco.  I'm gonna NACK on this.
>>>
>>> As I said: all use cases I particularly care about are covered by a
>>> global switch.
>>>
>>> I am laying down my views because I really believe they make more sense.
>>> But at some point, of course, I'll shut up if I believe I am a lone voice.
>>>
>>> I believe it should still be good to hear from mhocko and kame, but from
>>> your point of view, would all the rest, plus the introduction of a
>>> global switch make it acceptable to you?
>>
>> The only thing I'm whining about is per-node switch + silently
>> ignoring past accounting, so if those two are solved, I think I'm
>> pretty happy with the rest.
> 
> I think that per-group "switch" is not nice as well but if we make it
> hierarchy specific (which I am proposing for quite some time) and do not
> let enable accounting for a group with tasks then we get both
> flexibility and reasonable semantic. A global switch sounds too coars to
> me and it really not necessary.
> 
> Would this work with you?
> 

How exactly would that work? AFAIK, we have a single memcg root, we
can't have multiple memcg hierarchies in a system. Am I missing something?


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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Michal Hocko]

On Thu 27-09-12 16:20:55, Glauber Costa wrote:
> On 09/27/2012 04:15 PM, Michal Hocko wrote:
> > On Wed 26-09-12 16:33:34, Tejun Heo wrote:
> > [...]
> >>>> So, this seems properly crazy to me at the similar level of
> >>>> use_hierarchy fiasco.  I'm gonna NACK on this.
> >>>
> >>> As I said: all use cases I particularly care about are covered by a
> >>> global switch.
> >>>
> >>> I am laying down my views because I really believe they make more sense.
> >>> But at some point, of course, I'll shut up if I believe I am a lone voice.
> >>>
> >>> I believe it should still be good to hear from mhocko and kame, but from
> >>> your point of view, would all the rest, plus the introduction of a
> >>> global switch make it acceptable to you?
> >>
> >> The only thing I'm whining about is per-node switch + silently
> >> ignoring past accounting, so if those two are solved, I think I'm
> >> pretty happy with the rest.
> > 
> > I think that per-group "switch" is not nice as well but if we make it
> > hierarchy specific (which I am proposing for quite some time) and do not
> > let enable accounting for a group with tasks then we get both
> > flexibility and reasonable semantic. A global switch sounds too coars to
> > me and it really not necessary.
> > 
> > Would this work with you?
> > 
> 
> How exactly would that work? AFAIK, we have a single memcg root, we
> can't have multiple memcg hierarchies in a system. Am I missing something?

Well root is so different that we could consider the first level as the
real roots for hierarchies.
-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/27/2012 04:40 PM, Michal Hocko wrote:
> On Thu 27-09-12 16:20:55, Glauber Costa wrote:
>> On 09/27/2012 04:15 PM, Michal Hocko wrote:
>>> On Wed 26-09-12 16:33:34, Tejun Heo wrote:
>>> [...]
>>>>>> So, this seems properly crazy to me at the similar level of
>>>>>> use_hierarchy fiasco.  I'm gonna NACK on this.
>>>>>
>>>>> As I said: all use cases I particularly care about are covered by a
>>>>> global switch.
>>>>>
>>>>> I am laying down my views because I really believe they make more sense.
>>>>> But at some point, of course, I'll shut up if I believe I am a lone voice.
>>>>>
>>>>> I believe it should still be good to hear from mhocko and kame, but from
>>>>> your point of view, would all the rest, plus the introduction of a
>>>>> global switch make it acceptable to you?
>>>>
>>>> The only thing I'm whining about is per-node switch + silently
>>>> ignoring past accounting, so if those two are solved, I think I'm
>>>> pretty happy with the rest.
>>>
>>> I think that per-group "switch" is not nice as well but if we make it
>>> hierarchy specific (which I am proposing for quite some time) and do not
>>> let enable accounting for a group with tasks then we get both
>>> flexibility and reasonable semantic. A global switch sounds too coars to
>>> me and it really not necessary.
>>>
>>> Would this work with you?
>>>
>>
>> How exactly would that work? AFAIK, we have a single memcg root, we
>> can't have multiple memcg hierarchies in a system. Am I missing something?
> 
> Well root is so different that we could consider the first level as the
> real roots for hierarchies.
> 
So let's favor clarity: What you are proposing is that the first level
can have a switch for that, and the first level only. Is that right ?

At first, I just want to understand what exactly is your proposal. This
is not an endorsement of lack thereof.

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Michal Hocko]

On Thu 27-09-12 16:40:03, Glauber Costa wrote:
> On 09/27/2012 04:40 PM, Michal Hocko wrote:
> > On Thu 27-09-12 16:20:55, Glauber Costa wrote:
> >> On 09/27/2012 04:15 PM, Michal Hocko wrote:
> >>> On Wed 26-09-12 16:33:34, Tejun Heo wrote:
> >>> [...]
> >>>>>> So, this seems properly crazy to me at the similar level of
> >>>>>> use_hierarchy fiasco.  I'm gonna NACK on this.
> >>>>>
> >>>>> As I said: all use cases I particularly care about are covered by a
> >>>>> global switch.
> >>>>>
> >>>>> I am laying down my views because I really believe they make more sense.
> >>>>> But at some point, of course, I'll shut up if I believe I am a lone voice.
> >>>>>
> >>>>> I believe it should still be good to hear from mhocko and kame, but from
> >>>>> your point of view, would all the rest, plus the introduction of a
> >>>>> global switch make it acceptable to you?
> >>>>
> >>>> The only thing I'm whining about is per-node switch + silently
> >>>> ignoring past accounting, so if those two are solved, I think I'm
> >>>> pretty happy with the rest.
> >>>
> >>> I think that per-group "switch" is not nice as well but if we make it
> >>> hierarchy specific (which I am proposing for quite some time) and do not
> >>> let enable accounting for a group with tasks then we get both
> >>> flexibility and reasonable semantic. A global switch sounds too coars to
> >>> me and it really not necessary.
> >>>
> >>> Would this work with you?
> >>>
> >>
> >> How exactly would that work? AFAIK, we have a single memcg root, we
> >> can't have multiple memcg hierarchies in a system. Am I missing something?
> > 
> > Well root is so different that we could consider the first level as the
> > real roots for hierarchies.
> > 
> So let's favor clarity: What you are proposing is that the first level
> can have a switch for that, and the first level only. Is that right ?

I do not want any more switches. I am fine with your "set the limit and
start accounting apprach" and then inherit the _internal_ flag down the
hierarchy.
If you are in a child and want to set the limit then you can do that
only if your parent is accounted already (so that you can have your own
limit). We will need the same thing for oom_controll and swappinness.
-- 
Michal Hocko
SUSE Labs

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Mel Gorman]

On Wed, Sep 26, 2012 at 04:08:07PM -0700, Tejun Heo wrote:
> Hello, Glauber.
> 
> On Thu, Sep 27, 2012 at 02:54:11AM +0400, Glauber Costa wrote:
> > I don't. Much has been said in the past about the problem of sharing. A
> > lot of the kernel objects are shared by nature, this is pretty much
> > unavoidable. The answer we have been giving to this inquiry, is that the
> > workloads (us) interested in kmem accounted tend to be quite local in
> > their file accesses (and other kernel objects as well).
> > 
> > It should be obvious that not all workloads are like this, and some of
> > them would actually prefer to have their umem limited only.
> > 
> > There is nothing unreasonable in tracking user memory only.
> > 
> > If we have a global switch for "tracking all kernel memory", who would
> > you account the objects that are heavily shared to? I solve this by not
> > tracking kernel memory for cgroups in such workloads. What do you propose?
> 
> One of the things wrong with that is that it exposes the limitation of
> the current implementation as interface to userland, which is never a
> good idea.

I think the limitations have been fairly clearly explained and any admin
using the interface is going to have *some* familiarity with the limitations.

> In addition, how is userland supposed to know which
> workload is shared kmem heavy or not? 

By using a bit of common sense.

An application may not be able to figure this out but the administrator
is going to be able to make a very educated guess. If processes running
within two containers are not sharing a filesystem hierarchy for example
then it'll be clear they are not sharing dentries.

If there was a suspicion they were then it could be analysed with
something like SystemTap probing when files are opened and see if files
are being opened that are shared between containers.

It's not super-easy but it's not impossible either and I fail to see why
it's such a big deal for you.

>Details like that are not even
> inherent to workloads.  It's highly dependent on kernel implementation
> which may change any day.  If we hit workloads like that the right
> thing to do is improving kmemcg so that such problems don't occur, not
> exposing another switch.
> 
> If we can't make that work in reasonable (doesn't have to be perfect)
> way, we might as well just give up on kmem controller.  If userland
> has to second-guess kernel implementation details to make use of it,
> it's useless.
> 
> > > Well, that's really playing with words.  Limit is per cgroup and
> > > before the limit is set for the first time, everything is accounted to
> > > something else.  How is that keeping track?
> > > 
> > 
> > Even after the limit is set, it is set only by workloads that want kmem
> > to be tracked. If you want to track it during the whole lifetime of the
> > cgroup, you switch it before you put tasks to it. What is so crazy about it?
> 
> The fact that the numbers don't really mean what they apparently
> should mean.
> 

I think it is a reasonable limitation that only some kernel allocations are
accounted for although I'll freely admit I'm not a cgroup or memcg user
either.

My understanding is that this comes down to cost -- accounting for the
kernel memory usage is expensive so it is limited only to the allocations
that are easy to abuse by an unprivileged process. Hence this is
initially concerned with stack pages with dentries and TCP usage to
follow in later patches.

Further I would expect that an administrator would be aware of these
limitations and set kmem_accounting at cgroup creation time before any
processes start. Maybe that should be enforced but it's not a
fundamental problem.

Due to the cost of accounting, I can see why it would be desirable to
enable kmem_accounting for some cgroup trees and not others. It is not
unreasonable to expect that an administrator might want to account within
one cgroup where processes are accessing millions of files without
impairing the performance of another cgroup that is mostly using
anonymous memory.

> > > The proposed behavior seems really crazy to me.  Do people really
> > > think this is a good idea?
> > 
> > It is really sad that you lost the opportunity to say that in a room
> > full of mm developers that could add to this discussion in real time,
> > when after an explanation about this was given, Mel asked if anyone
> > would have any objections to this.
> 
> Sure, conferences are useful for building consensus but that's the
> extent of it.  Sorry that I didn't realize the implications then but
> conferences don't really add any finality to decisions.
> 
> So, this seems properly crazy to me at the similar level of
> use_hierarchy fiasco.  I'm gonna NACK on this.
> 

I think you're over-reacting to say the very least :|

-- 
Mel Gorman
SUSE Labs

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Mel.

On Thu, Sep 27, 2012 at 03:28:22PM +0100, Mel Gorman wrote:
> > In addition, how is userland supposed to know which
> > workload is shared kmem heavy or not? 
> 
> By using a bit of common sense.
> 
> An application may not be able to figure this out but the administrator
> is going to be able to make a very educated guess. If processes running
> within two containers are not sharing a filesystem hierarchy for example
> then it'll be clear they are not sharing dentries.
> 
> If there was a suspicion they were then it could be analysed with
> something like SystemTap probing when files are opened and see if files
> are being opened that are shared between containers.
> 
> It's not super-easy but it's not impossible either and I fail to see why
> it's such a big deal for you.

Because we're not even trying to actually solve the problem but just
dumping it to userland.  If dentry/inode usage is the only case we're
being worried about, there can be better ways to solve it or at least
we should strive for that.

Also, the problem is not that it is impossible if you know and
carefully plan for things beforehand (that would be one extremely
competent admin) but that the problem is undiscoverable.  With kmemcg
accounting disabled, there's no way to tell a looking cgroup the admin
thinks running something which doesn'ft tax kmem much could be
generating a ton without the admin ever noticing.

> > The fact that the numbers don't really mean what they apparently
> > should mean.
> 
> I think it is a reasonable limitation that only some kernel allocations are
> accounted for although I'll freely admit I'm not a cgroup or memcg user
> either.
> 
> My understanding is that this comes down to cost -- accounting for the
> kernel memory usage is expensive so it is limited only to the allocations
> that are easy to abuse by an unprivileged process. Hence this is
> initially concerned with stack pages with dentries and TCP usage to
> follow in later patches.

I think the cost isn't too prohibitive considering it's already using
memcg.  Charging / uncharging happens only as pages enter and leave
slab caches and the hot path overhead is essentially single
indirection.  Glauber's benchmark seemed pretty reasonable to me and I
don't yet think that warrants exposing this subtle tree of
configuration.

> > Sure, conferences are useful for building consensus but that's the
> > extent of it.  Sorry that I didn't realize the implications then but
> > conferences don't really add any finality to decisions.
> > 
> > So, this seems properly crazy to me at the similar level of
> > use_hierarchy fiasco.  I'm gonna NACK on this.
> 
> I think you're over-reacting to say the very least :|

The part I nacked is enabling kmemcg on a populated cgroup and then
starting accounting from then without any apparent indication that any
past allocation hasn't been considered.  You end up with numbers which
nobody can't tell what they really mean and there's no mechanism to
guarantee any kind of ordering between populating the cgroup and
configuring it and there's *no* way to find out what happened
afterwards neither.  This is properly crazy and definitely deserves a
nack.

Thanks.

-- 
tejun

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/27/2012 06:49 PM, Tejun Heo wrote:
> Hello, Mel.
> 
> On Thu, Sep 27, 2012 at 03:28:22PM +0100, Mel Gorman wrote:
>>> In addition, how is userland supposed to know which
>>> workload is shared kmem heavy or not? 
>>
>> By using a bit of common sense.
>>
>> An application may not be able to figure this out but the administrator
>> is going to be able to make a very educated guess. If processes running
>> within two containers are not sharing a filesystem hierarchy for example
>> then it'll be clear they are not sharing dentries.
>>
>> If there was a suspicion they were then it could be analysed with
>> something like SystemTap probing when files are opened and see if files
>> are being opened that are shared between containers.
>>
>> It's not super-easy but it's not impossible either and I fail to see why
>> it's such a big deal for you.
> 
> Because we're not even trying to actually solve the problem but just
> dumping it to userland.  If dentry/inode usage is the only case we're
> being worried about, there can be better ways to solve it or at least
> we should strive for that.
> 

Not only it is not the only case we care about, this is not even touched
in this series. (It is only touched in the next one). This one, for
instance, cares about the stack. The reason everything is being dumped
into "kmem", is precisely to make things simpler. I argue that at some
point it makes sense to draw a line, and "kmem" is a much better line
than any fine grained control - precisely because it is conceptually
easier to grasp.


> Also, the problem is not that it is impossible if you know and
> carefully plan for things beforehand (that would be one extremely
> competent admin) but that the problem is undiscoverable.  With kmemcg
> accounting disabled, there's no way to tell a looking cgroup the admin
> thinks running something which doesn'ft tax kmem much could be
> generating a ton without the admin ever noticing.
> 
>>> The fact that the numbers don't really mean what they apparently
>>> should mean.
>>
>> I think it is a reasonable limitation that only some kernel allocations are
>> accounted for although I'll freely admit I'm not a cgroup or memcg user
>> either.
>>
>> My understanding is that this comes down to cost -- accounting for the
>> kernel memory usage is expensive so it is limited only to the allocations
>> that are easy to abuse by an unprivileged process. Hence this is
>> initially concerned with stack pages with dentries and TCP usage to
>> follow in later patches.
> 
> I think the cost isn't too prohibitive considering it's already using
> memcg.  Charging / uncharging happens only as pages enter and leave
> slab caches and the hot path overhead is essentially single
> indirection.  Glauber's benchmark seemed pretty reasonable to me and I
> don't yet think that warrants exposing this subtle tree of
> configuration.
> 

Only so we can get some numbers: the cost is really minor if this is all
disabled. It this is fully enable, it can get to some 2 or 3 %, which
may or may not be acceptable to an application. But for me this is not
even about cost, and that's why I haven't brought it up so far

>>> Sure, conferences are useful for building consensus but that's the
>>> extent of it.  Sorry that I didn't realize the implications then but
>>> conferences don't really add any finality to decisions.
>>>
>>> So, this seems properly crazy to me at the similar level of
>>> use_hierarchy fiasco.  I'm gonna NACK on this.
>>
>> I think you're over-reacting to say the very least :|
> 
> The part I nacked is enabling kmemcg on a populated cgroup and then
> starting accounting from then without any apparent indication that any
> past allocation hasn't been considered.  You end up with numbers which
> nobody can't tell what they really mean and there's no mechanism to
> guarantee any kind of ordering between populating the cgroup and
> configuring it and there's *no* way to find out what happened
> afterwards neither.  This is properly crazy and definitely deserves a
> nack.
> 

Mel suggestion of not allowing this to happen once the cgroup has tasks
takes care of this, and is something I thought of myself.

This would remove this particular piece of objection, and maintain the
per-subtree control.

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello,

On Thu, Sep 27, 2012 at 06:57:59PM +0400, Glauber Costa wrote:
> > Because we're not even trying to actually solve the problem but just
> > dumping it to userland.  If dentry/inode usage is the only case we're
> > being worried about, there can be better ways to solve it or at least
> > we should strive for that.
> 
> Not only it is not the only case we care about, this is not even touched
> in this series. (It is only touched in the next one). This one, for
> instance, cares about the stack. The reason everything is being dumped
> into "kmem", is precisely to make things simpler. I argue that at some
> point it makes sense to draw a line, and "kmem" is a much better line
> than any fine grained control - precisely because it is conceptually
> easier to grasp.

Can you please give other examples of cases where this type of issue
exists (plenty of shared kernel data structure which is inherent to
the workload at hand)?  Until now, this has been the only example for
this type of issues.

> > I think the cost isn't too prohibitive considering it's already using
> > memcg.  Charging / uncharging happens only as pages enter and leave
> > slab caches and the hot path overhead is essentially single
> > indirection.  Glauber's benchmark seemed pretty reasonable to me and I
> > don't yet think that warrants exposing this subtle tree of
> > configuration.
> 
> Only so we can get some numbers: the cost is really minor if this is all
> disabled. It this is fully enable, it can get to some 2 or 3 %, which
> may or may not be acceptable to an application. But for me this is not
> even about cost, and that's why I haven't brought it up so far

It seems like Mel's concern is mostly based on performance overhead
concerns tho.

> > The part I nacked is enabling kmemcg on a populated cgroup and then
> > starting accounting from then without any apparent indication that any
> > past allocation hasn't been considered.  You end up with numbers which
> > nobody can't tell what they really mean and there's no mechanism to
> > guarantee any kind of ordering between populating the cgroup and
> > configuring it and there's *no* way to find out what happened
> > afterwards neither.  This is properly crazy and definitely deserves a
> > nack.
> > 
> 
> Mel suggestion of not allowing this to happen once the cgroup has tasks
> takes care of this, and is something I thought of myself.

You mean Michal's?  It should also disallow switching if there are
children cgroups, right?

> This would remove this particular piece of objection, and maintain the
> per-subtree control.

Yeah, I don't see anything broken with that although I'll try to argue
for simpler one a bit more.

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Michal Hocko]

On Thu 27-09-12 10:46:05, Tejun Heo wrote:
[...]
> > > The part I nacked is enabling kmemcg on a populated cgroup and then
> > > starting accounting from then without any apparent indication that any
> > > past allocation hasn't been considered.  You end up with numbers which
> > > nobody can't tell what they really mean and there's no mechanism to
> > > guarantee any kind of ordering between populating the cgroup and
> > > configuring it and there's *no* way to find out what happened
> > > afterwards neither.  This is properly crazy and definitely deserves a
> > > nack.
> > > 
> > 
> > Mel suggestion of not allowing this to happen once the cgroup has tasks
> > takes care of this, and is something I thought of myself.
> 
> You mean Michal's?  It should also disallow switching if there are
> children cgroups, right?

Right.
 
-- 
Michal Hocko
SUSE Labs

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/27/2012 09:46 PM, Tejun Heo wrote:
> Hello,
> 
> On Thu, Sep 27, 2012 at 06:57:59PM +0400, Glauber Costa wrote:
>>> Because we're not even trying to actually solve the problem but just
>>> dumping it to userland.  If dentry/inode usage is the only case we're
>>> being worried about, there can be better ways to solve it or at least
>>> we should strive for that.
>>
>> Not only it is not the only case we care about, this is not even touched
>> in this series. (It is only touched in the next one). This one, for
>> instance, cares about the stack. The reason everything is being dumped
>> into "kmem", is precisely to make things simpler. I argue that at some
>> point it makes sense to draw a line, and "kmem" is a much better line
>> than any fine grained control - precisely because it is conceptually
>> easier to grasp.
> 
> Can you please give other examples of cases where this type of issue
> exists (plenty of shared kernel data structure which is inherent to
> the workload at hand)?  Until now, this has been the only example for
> this type of issues.
> 

Yes. the namespace related caches (*), all kinds of sockets and network
structures, other file system structures like file struct, vm areas, and
pretty much everything a full container does.

(*) we run full userspace, so we have namespaces + cgroups combination.

>>> I think the cost isn't too prohibitive considering it's already using
>>> memcg.  Charging / uncharging happens only as pages enter and leave
>>> slab caches and the hot path overhead is essentially single
>>> indirection.  Glauber's benchmark seemed pretty reasonable to me and I
>>> don't yet think that warrants exposing this subtle tree of
>>> configuration.
>>
>> Only so we can get some numbers: the cost is really minor if this is all
>> disabled. It this is fully enable, it can get to some 2 or 3 %, which
>> may or may not be acceptable to an application. But for me this is not
>> even about cost, and that's why I haven't brought it up so far
> 
> It seems like Mel's concern is mostly based on performance overhead
> concerns tho.
> 
>>> The part I nacked is enabling kmemcg on a populated cgroup and then
>>> starting accounting from then without any apparent indication that any
>>> past allocation hasn't been considered.  You end up with numbers which
>>> nobody can't tell what they really mean and there's no mechanism to
>>> guarantee any kind of ordering between populating the cgroup and
>>> configuring it and there's *no* way to find out what happened
>>> afterwards neither.  This is properly crazy and definitely deserves a
>>> nack.
>>>
>>
>> Mel suggestion of not allowing this to happen once the cgroup has tasks
>> takes care of this, and is something I thought of myself.
> 
> You mean Michal's?  It should also disallow switching if there are
> children cgroups, right?
> 

No, I meant Mel, quoting this:

"Further I would expect that an administrator would be aware of these
limitations and set kmem_accounting at cgroup creation time before any
processes start. Maybe that should be enforced but it's not a
fundamental problem."

But I guess it is pretty much the same thing Michal proposes, in essence.

Or IOW, if your concern is with the fact that charges may have happened
in the past before this is enabled, we can make sure this cannot happen
by disallowing the limit to be set if currently unset (value changes are
obviously fine) if you have children or any tasks already in the group.

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Glauber.

On Thu, Sep 27, 2012 at 10:45:01PM +0400, Glauber Costa wrote:
> > Can you please give other examples of cases where this type of issue
> > exists (plenty of shared kernel data structure which is inherent to
> > the workload at hand)?  Until now, this has been the only example for
> > this type of issues.
> 
> Yes. the namespace related caches (*), all kinds of sockets and network
> structures, other file system structures like file struct, vm areas, and
> pretty much everything a full container does.
> 
> (*) we run full userspace, so we have namespaces + cgroups combination.

This is probably me being dumb but wouldn't resources used by full
namespaces be mostly independent?  Which parts get shared?  Also, if
you do full namespace, isn't it more likely that you would want fuller
resource isolation too?

> >> Mel suggestion of not allowing this to happen once the cgroup has tasks
> >> takes care of this, and is something I thought of myself.
> > 
> > You mean Michal's?  It should also disallow switching if there are
> > children cgroups, right?
> 
> No, I meant Mel, quoting this:
> 
> "Further I would expect that an administrator would be aware of these
> limitations and set kmem_accounting at cgroup creation time before any
> processes start. Maybe that should be enforced but it's not a
> fundamental problem."
> 
> But I guess it is pretty much the same thing Michal proposes, in essence.
> 
> Or IOW, if your concern is with the fact that charges may have happened
> in the past before this is enabled, we can make sure this cannot happen
> by disallowing the limit to be set if currently unset (value changes are
> obviously fine) if you have children or any tasks already in the group.

Yeah, please do that.

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

On Sun, Sep 30, 2012 at 04:57:00PM +0900, Tejun Heo wrote:
> On Thu, Sep 27, 2012 at 10:45:01PM +0400, Glauber Costa wrote:
> > > Can you please give other examples of cases where this type of issue
> > > exists (plenty of shared kernel data structure which is inherent to
> > > the workload at hand)?  Until now, this has been the only example for
> > > this type of issues.
> > 
> > Yes. the namespace related caches (*), all kinds of sockets and network
> > structures, other file system structures like file struct, vm areas, and
> > pretty much everything a full container does.
> > 
> > (*) we run full userspace, so we have namespaces + cgroups combination.
> 
> This is probably me being dumb but wouldn't resources used by full
> namespaces be mostly independent?  Which parts get shared?  Also, if
> you do full namespace, isn't it more likely that you would want fuller
> resource isolation too?

Just a thought about dentry/inode.  Would it make sense to count total
number of references per cgroup and charge the total amount according
to that?  Reference counts are how the shared ownership is represented
after all.  Counting total per cgroup isn't accurate and pathological
cases could be weird tho.

Thanks.

-- 
tejun

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[James Bottomley]

On Sun, 2012-09-30 at 17:02 +0900, Tejun Heo wrote:
> On Sun, Sep 30, 2012 at 04:57:00PM +0900, Tejun Heo wrote:
> > On Thu, Sep 27, 2012 at 10:45:01PM +0400, Glauber Costa wrote:
> > > > Can you please give other examples of cases where this type of issue
> > > > exists (plenty of shared kernel data structure which is inherent to
> > > > the workload at hand)?  Until now, this has been the only example for
> > > > this type of issues.
> > > 
> > > Yes. the namespace related caches (*), all kinds of sockets and network
> > > structures, other file system structures like file struct, vm areas, and
> > > pretty much everything a full container does.
> > > 
> > > (*) we run full userspace, so we have namespaces + cgroups combination.
> > 
> > This is probably me being dumb but wouldn't resources used by full
> > namespaces be mostly independent?  Which parts get shared?  Also, if
> > you do full namespace, isn't it more likely that you would want fuller
> > resource isolation too?
> 
> Just a thought about dentry/inode.  Would it make sense to count total
> number of references per cgroup and charge the total amount according
> to that?  Reference counts are how the shared ownership is represented
> after all.  Counting total per cgroup isn't accurate and pathological
> cases could be weird tho.

The beancounter approach originally used by OpenVZ does exactly this.
There are two specific problems, though, firstly you can't count
references in generic code, so now you have to extend the cgroup
tentacles into every object, an invasiveness which people didn't really
like.  Secondly split accounting causes oddities too, like your total
kernel memory usage can appear to go down even though you do nothing
just because someone else added a share.  Worse, if someone drops the
reference, your usage can go up, even though you did nothing, and push
you over your limit, at which point action gets taken against the
container.  This leads to nasty system unpredictability (The whole point
of cgroup isolation is supposed to be preventing resource usage in one
cgroup from affecting that in another).

We discussed this pretty heavily at the Containers Mini Summit in Santa
Rosa.  The emergent consensus was that no-one really likes first use
accounting, but it does solve all the problems and it has the fewest
unexpected side effects.

If you have an alternative that wasn't considered then, I'm sure
everyone would be interested, but it isn't split accounting.

James

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, James.

On Sun, Sep 30, 2012 at 09:56:28AM +0100, James Bottomley wrote:
> The beancounter approach originally used by OpenVZ does exactly this.
> There are two specific problems, though, firstly you can't count
> references in generic code, so now you have to extend the cgroup
> tentacles into every object, an invasiveness which people didn't really
> like.

Yeah, it will need some hooks.  For dentry and inode, I think it would
be pretty well isolated tho.  Wasn't it?

> Secondly split accounting causes oddities too, like your total
> kernel memory usage can appear to go down even though you do nothing
> just because someone else added a share.  Worse, if someone drops the
> reference, your usage can go up, even though you did nothing, and push
> you over your limit, at which point action gets taken against the
> container.  This leads to nasty system unpredictability (The whole point
> of cgroup isolation is supposed to be preventing resource usage in one
> cgroup from affecting that in another).

In a sense, the fluctuating amount is the actual resource burden the
cgroup is putting on the system, so maybe it just needs to be handled
better or maybe we should charge fixed amount per refcnt?  I don't
know.

> We discussed this pretty heavily at the Containers Mini Summit in Santa
> Rosa.  The emergent consensus was that no-one really likes first use
> accounting, but it does solve all the problems and it has the fewest
> unexpected side effects.

But that's like fitting the problem to the mechanism.  Maybe that is
the best which can be done, but the side effect there is way-off
accounting under pretty common workload, which sounds pretty nasty to
me.

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[James Bottomley]

On Sun, 2012-09-30 at 19:37 +0900, Tejun Heo wrote:
> Hello, James.
> 
> On Sun, Sep 30, 2012 at 09:56:28AM +0100, James Bottomley wrote:
> > The beancounter approach originally used by OpenVZ does exactly this.
> > There are two specific problems, though, firstly you can't count
> > references in generic code, so now you have to extend the cgroup
> > tentacles into every object, an invasiveness which people didn't really
> > like.
> 
> Yeah, it will need some hooks.  For dentry and inode, I think it would
> be pretty well isolated tho.  Wasn't it?

But you've got to ask yourself who cares about accurate accounting per
container of dentry and inode objects? They're not objects that any
administrator is used to limiting.  What we at parallels care about
isn't accurately accounting them, it's that one container can't DoS
another by exhausting system resources.  That's achieved equally well by
first charge slab accounting, so we don't really have an interest in
pushing object accounting code for which there's no use case.

> > Secondly split accounting causes oddities too, like your total
> > kernel memory usage can appear to go down even though you do nothing
> > just because someone else added a share.  Worse, if someone drops the
> > reference, your usage can go up, even though you did nothing, and push
> > you over your limit, at which point action gets taken against the
> > container.  This leads to nasty system unpredictability (The whole point
> > of cgroup isolation is supposed to be preventing resource usage in one
> > cgroup from affecting that in another).
> 
> In a sense, the fluctuating amount is the actual resource burden the
> cgroup is putting on the system, so maybe it just needs to be handled
> better or maybe we should charge fixed amount per refcnt?  I don't
> know.

Yes, we considered single charge per reference accounting as well
(although I don't believe anyone went as far as producing an
implementation).  The problem here is now that the sum of the container
resources no-longer bears any relation to the host consumption.  This
makes it very difficult for virtualisation orchestration systems to make
accurate decisions when doing dynamic resource scheduling (DRS).

Conversely, as ugly as you think it, first use accounting is actually
pretty good at identifying problem containers (at least with regard to
memory usage) for DRS because containers which are stretching the memory
tend to accumulate the greatest number of first charges over the system
lifetime.

> > We discussed this pretty heavily at the Containers Mini Summit in Santa
> > Rosa.  The emergent consensus was that no-one really likes first use
> > accounting, but it does solve all the problems and it has the fewest
> > unexpected side effects.
> 
> But that's like fitting the problem to the mechanism.  Maybe that is
> the best which can be done, but the side effect there is way-off
> accounting under pretty common workload, which sounds pretty nasty to
> me.

All we need kernel memory accounting and limiting for is DoS prevention.
There aren't really any system administrators who care about Kernel
Memory accounting (at least until the system goes oom) because there are
no absolute knobs for it (all there is are a set of weird and wonderful
heuristics, like dirty limit ratio and drop caches).  Kernel memory
usage has a whole set of regulatory infrastructure for trying to make it
transparent to the user.

Don't get me wrong: if there were some easy way to get proper memory
accounting for free, we'd be happy but, because it has no practical
application for any of our customers, there's a limited price we're
willing to pay to get it.

James

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, James.

On Sun, Sep 30, 2012 at 12:25:52PM +0100, James Bottomley wrote:
> But you've got to ask yourself who cares about accurate accounting per
> container of dentry and inode objects? They're not objects that any
> administrator is used to limiting.  What we at parallels care about
> isn't accurately accounting them, it's that one container can't DoS
> another by exhausting system resources.  That's achieved equally well by
> first charge slab accounting, so we don't really have an interest in
> pushing object accounting code for which there's no use case.

Isn't it more because the use cases you have on mind don't share
dentries/inodes too much?  Wildly incorrect accounting definitely
degrades container isolation and can lead to unexpected behaviors.

> All we need kernel memory accounting and limiting for is DoS prevention.
> There aren't really any system administrators who care about Kernel
> Memory accounting (at least until the system goes oom) because there are
> no absolute knobs for it (all there is are a set of weird and wonderful
> heuristics, like dirty limit ratio and drop caches).  Kernel memory

I think that's because the mechanism currently doesn't exist.  If one
wants to control how memory is distributed across different cgroups,
it's logical to control kernel memory too.  The resource in question
is the actual memory after all.  I think at least google would be
interested in it, so, no, I don't agree that nobody wants it.  If that
is the case, we're working towards the wrong direction.

> usage has a whole set of regulatory infrastructure for trying to make it
> transparent to the user.
> 
> Don't get me wrong: if there were some easy way to get proper memory
> accounting for free, we'd be happy but, because it has no practical
> application for any of our customers, there's a limited price we're
> willing to pay to get it.

Even on purely technical ground, it could be that first-use is the
right trade off if other more accurate approaches are too difficult
and most workloads are happy with such approach.  I'm still a bit
weary to base userland interface decisions on that tho.

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 10/01/2012 04:57 AM, Tejun Heo wrote:
> Hello, James.
> 
> On Sun, Sep 30, 2012 at 12:25:52PM +0100, James Bottomley wrote:
>> But you've got to ask yourself who cares about accurate accounting per
>> container of dentry and inode objects? They're not objects that any
>> administrator is used to limiting.  What we at parallels care about
>> isn't accurately accounting them, it's that one container can't DoS
>> another by exhausting system resources.  That's achieved equally well by
>> first charge slab accounting, so we don't really have an interest in
>> pushing object accounting code for which there's no use case.
> 
> Isn't it more because the use cases you have on mind don't share
> dentries/inodes too much?  Wildly incorrect accounting definitely
> degrades container isolation and can lead to unexpected behaviors.
> 
>> All we need kernel memory accounting and limiting for is DoS prevention.
>> There aren't really any system administrators who care about Kernel
>> Memory accounting (at least until the system goes oom) because there are
>> no absolute knobs for it (all there is are a set of weird and wonderful
>> heuristics, like dirty limit ratio and drop caches).  Kernel memory
> 
> I think that's because the mechanism currently doesn't exist.  If one
> wants to control how memory is distributed across different cgroups,
> it's logical to control kernel memory too.  The resource in question
> is the actual memory after all.  I think at least google would be
> interested in it, so, no, I don't agree that nobody wants it.  If that
> is the case, we're working towards the wrong direction.
> 
>> usage has a whole set of regulatory infrastructure for trying to make it
>> transparent to the user.
>>
>> Don't get me wrong: if there were some easy way to get proper memory
>> accounting for free, we'd be happy but, because it has no practical
>> application for any of our customers, there's a limited price we're
>> willing to pay to get it.
> 
> Even on purely technical ground, it could be that first-use is the
> right trade off if other more accurate approaches are too difficult
> and most workloads are happy with such approach.  I'm still a bit
> weary to base userland interface decisions on that tho.
> 

For the record, user memory also suffers a bit from being always
constrained to first-touch accounting. Greg Thelen is working on
alternative solutions to make first-accounting the default in a
configurable environment, as he explained in the kernel summit.

When that happens, kernel memory can take advantage of it for free.

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/30/2012 02:37 PM, Tejun Heo wrote:
> Hello, James.
> 
> On Sun, Sep 30, 2012 at 09:56:28AM +0100, James Bottomley wrote:
>> The beancounter approach originally used by OpenVZ does exactly this.
>> There are two specific problems, though, firstly you can't count
>> references in generic code, so now you have to extend the cgroup
>> tentacles into every object, an invasiveness which people didn't really
>> like.
> 
> Yeah, it will need some hooks.  For dentry and inode, I think it would
> be pretty well isolated tho.  Wasn't it?
> 

We would still need something for the stack. For open files, and for
everything that becomes a potential problem. We then end up with 35
different knobs instead of one. One of the perceived advantages of this
approach, is that it condenses as much data as a single knob as
possible, reducing complexity and over flexibility.

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Glauber.

On Mon, Oct 01, 2012 at 12:46:02PM +0400, Glauber Costa wrote:
> > Yeah, it will need some hooks.  For dentry and inode, I think it would
> > be pretty well isolated tho.  Wasn't it?
> 
> We would still need something for the stack. For open files, and for
> everything that becomes a potential problem. We then end up with 35
> different knobs instead of one. One of the perceived advantages of this
> approach, is that it condenses as much data as a single knob as
> possible, reducing complexity and over flexibility.

Oh, I didn't mean to use object-specific counting for all of them.
Most resources don't have such common misaccounting problem.  I mean,
for stack, it doesn't exist by definition (other than cgroup
migration).  There's no reason to use anything other than first-use
kmem based accounting for them.  My point was that for particularly
problematic ones like dentry/inode, it might be better to treat them
differently.

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/30/2012 11:57 AM, Tejun Heo wrote:
> Hello, Glauber.
> 
> On Thu, Sep 27, 2012 at 10:45:01PM +0400, Glauber Costa wrote:
>>> Can you please give other examples of cases where this type of issue
>>> exists (plenty of shared kernel data structure which is inherent to
>>> the workload at hand)?  Until now, this has been the only example for
>>> this type of issues.
>>
>> Yes. the namespace related caches (*), all kinds of sockets and network
>> structures, other file system structures like file struct, vm areas, and
>> pretty much everything a full container does.
>>
>> (*) we run full userspace, so we have namespaces + cgroups combination.
> 
> This is probably me being dumb but wouldn't resources used by full
> namespaces be mostly independent?  Which parts get shared?  Also, if
> you do full namespace, isn't it more likely that you would want fuller
> resource isolation too?
> 

Not necessarily. Namespaces are pretty flexible. If you are using the
network namespace, for instance, you can create interfaces, routes,
addresses, etc. But because this deals with the network only, there is
nothing unreasonable in saying that your webserver and database lives in
the same network (which is a different network namespace), but are
entitled to different memory limits - which is cgroups realm. With
application-only containers being championed these days by multiple
users, I would expect this situation to become non-negligible.

The full container scenario, of course, is very different. Most of the
accesses tends to be local.

I will second what Michal said, since I believe this is also very
important: User memory is completely at the control of the application,
while kernel memory is not, and never will. It is perfectly fine to
imagine applications that want its memory to be limited by a very
predictable amount, and there are no reasons to believe that those
cannot live in the same box as full containers - the biggest example of
kmem interested folks. It could be, for instance, that a management tool
for containers lives in there, and that application wants to be umem
limited but not kmem limited. (If it goes touching files and data inside
each container, for instance, it is obviously not local)

>>>> Mel suggestion of not allowing this to happen once the cgroup has tasks
>>>> takes care of this, and is something I thought of myself.
>>>
>>> You mean Michal's?  It should also disallow switching if there are
>>> children cgroups, right?
>>
>> No, I meant Mel, quoting this:
>>
>> "Further I would expect that an administrator would be aware of these
>> limitations and set kmem_accounting at cgroup creation time before any
>> processes start. Maybe that should be enforced but it's not a
>> fundamental problem."
>>
>> But I guess it is pretty much the same thing Michal proposes, in essence.
>>
>> Or IOW, if your concern is with the fact that charges may have happened
>> in the past before this is enabled, we can make sure this cannot happen
>> by disallowing the limit to be set if currently unset (value changes are
>> obviously fine) if you have children or any tasks already in the group.
> 
> Yeah, please do that.
> 

I did already, patches soon! =)

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Michal Hocko]

On Thu 27-09-12 01:24:40, Glauber Costa wrote:
[...]
> About use cases, I've already responded: my containers use case is kmem
> limited. There are people like Michal that specifically asked for
> user-only semantics to be preserved. 

Yes, because we have many users (basically almost all) who care only
about the user memory because that's what occupies the vast majority of
the memory. They usually want to isolate workload which would disrupt
the global memory otherwise (e.g. backup process vs. database). You
really do not want to pay an additional overhead for kmem accounting
here.

> So your question for global vs local switch (that again, doesn't
> exist; only a local *limit* exists) should really be posed in the
> following way:  "Can two different use cases with different needs be
> hosted in the same box?"

I think this is a good and a relevant question. I think this boils down
to whether you want to have trusted and untrusted workloads at the same
machine.
Trusted loads usually only need user memory accounting because kmem
consumption should be really negligible (unless kernel is doing
something really stupid and no kmem limit will help here). 
On the other hand, untrusted workloads can do nasty things that
administrator has hard time to mitigate and setting a kmem limit can
help significantly.

IMHO such a different loads exist on a single machine quite often (Web
server and a back up process as the most simplistic one). The per
hierarchy accounting, therefore, sounds like a good idea without too
much added complexity (actually the only added complexity is in the
proper kmem.limit_in_bytes handling which is a single place).

So I would rather go with per-hierarchy thing.

> > Michal, Johannes, Kamezawa, what are your thoughts?
> >
> waiting! =)

Well, you guys generated a lot of discussion that one has to read
through, didn't you :P

-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

>>> Michal, Johannes, Kamezawa, what are your thoughts?
>>>
>> waiting! =)
> 
> Well, you guys generated a lot of discussion that one has to read
> through, didn't you :P
> 
We're quite good at that!


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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Michal.

On Thu, Sep 27, 2012 at 02:08:06PM +0200, Michal Hocko wrote:
> Yes, because we have many users (basically almost all) who care only
> about the user memory because that's what occupies the vast majority of
> the memory. They usually want to isolate workload which would disrupt
> the global memory otherwise (e.g. backup process vs. database). You
> really do not want to pay an additional overhead for kmem accounting
> here.

I'm not too convinced.  First of all, the overhead added by kmemcg
isn't big.  The hot path overhead is quite minimal - it doesn't do
much more than indirecting one more time.  In terms of memory usage,
it sure could lead to a bit more fragmentation but even if it gets to
several megs per cgroup, I don't think that's something excessive.
So, there is overhead but I don't believe it to be prohibitive.

> > So your question for global vs local switch (that again, doesn't
> > exist; only a local *limit* exists) should really be posed in the
> > following way:  "Can two different use cases with different needs be
> > hosted in the same box?"
> 
> I think this is a good and a relevant question. I think this boils down
> to whether you want to have trusted and untrusted workloads at the same
> machine.
> Trusted loads usually only need user memory accounting because kmem
> consumption should be really negligible (unless kernel is doing
> something really stupid and no kmem limit will help here). 
> On the other hand, untrusted workloads can do nasty things that
> administrator has hard time to mitigate and setting a kmem limit can
> help significantly.
> 
> IMHO such a different loads exist on a single machine quite often (Web
> server and a back up process as the most simplistic one). The per
> hierarchy accounting, therefore, sounds like a good idea without too
> much added complexity (actually the only added complexity is in the
> proper kmem.limit_in_bytes handling which is a single place).

The distinction between "trusted" and "untrusted" is something
artificially created due to the assumed deficiency of kmemcg
implementation.  Making things like this visible to userland is a bad
idea because it locks us into a place where we can't or don't need to
improve the said deficiencies and end up pushing the difficult
problems to somewhere else where it will likely be implemented in a
shabbier way.  There sure are cases when such approach simply cannot
be avoided, but I really don't think that's the case here - the
overhead already seems to be at an acceptable level and we're not
taking away the escape switch.

This is userland visible API.  We better err on the side of being
conservative than going overboard with flexibility.  Even if we
eventually need to make this switching fullly hierarchical, we really
should be doing,

1. Implement simple global switching and look for problem cases.

2. Analyze them and see whether the problem case can't be solved in a
   better, more intelligent way.

3. If the problem is something structurally inherent or reasonably too
   difficult to solve any other way, consider dumping the problem as
   config parameters to userland.

We can always expand the flexibility.  Let's do the simple thing
first.  As an added bonus, it would enable using static_keys for
accounting branches too.

Thanks.

-- 
tejun

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Mel Gorman]

On Thu, Sep 27, 2012 at 07:33:00AM -0700, Tejun Heo wrote:
> Hello, Michal.
> 
> On Thu, Sep 27, 2012 at 02:08:06PM +0200, Michal Hocko wrote:
> > Yes, because we have many users (basically almost all) who care only
> > about the user memory because that's what occupies the vast majority of
> > the memory. They usually want to isolate workload which would disrupt
> > the global memory otherwise (e.g. backup process vs. database). You
> > really do not want to pay an additional overhead for kmem accounting
> > here.
> 
> I'm not too convinced.  First of all, the overhead added by kmemcg
> isn't big. 

Really?

If kmemcg was globally accounted then every __GFP_KMEMCG allocation in
the page allocator potentially ends up down in
__memcg_kmem_newpage_charge which

1. takes RCU read lock
2. looks up cgroup from task
3. takes a reference count
4. memcg_charge_kmem -> __mem_cgroup_try_charge
5. release reference count

That's a *LOT* of work to incur for cgroups that do not care about kernel
accounting. This is why I thought it was reasonable that the kmem accounting
not be global.

-- 
Mel Gorman
SUSE Labs

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Mel.

On Thu, Sep 27, 2012 at 03:43:07PM +0100, Mel Gorman wrote:
> > I'm not too convinced.  First of all, the overhead added by kmemcg
> > isn't big. 
> 
> Really?
> 
> If kmemcg was globally accounted then every __GFP_KMEMCG allocation in
> the page allocator potentially ends up down in
> __memcg_kmem_newpage_charge which
> 
> 1. takes RCU read lock
> 2. looks up cgroup from task
> 3. takes a reference count
> 4. memcg_charge_kmem -> __mem_cgroup_try_charge
> 5. release reference count
> 
> That's a *LOT* of work to incur for cgroups that do not care about kernel
> accounting. This is why I thought it was reasonable that the kmem accounting
> not be global.

But that happens only when pages enter and leave slab and if it still
is significant, we can try to further optimize charging.  Given that
this is only for cases where memcg is already in use and we provide a
switch to disable it globally, I really don't think this warrants
implementing fully hierarchy configuration.

Thanks.

-- 
tejun

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/27/2012 06:58 PM, Tejun Heo wrote:
> Hello, Mel.
> 
> On Thu, Sep 27, 2012 at 03:43:07PM +0100, Mel Gorman wrote:
>>> I'm not too convinced.  First of all, the overhead added by kmemcg
>>> isn't big. 
>>
>> Really?
>>
>> If kmemcg was globally accounted then every __GFP_KMEMCG allocation in
>> the page allocator potentially ends up down in
>> __memcg_kmem_newpage_charge which
>>
>> 1. takes RCU read lock
>> 2. looks up cgroup from task
>> 3. takes a reference count
>> 4. memcg_charge_kmem -> __mem_cgroup_try_charge
>> 5. release reference count
>>
>> That's a *LOT* of work to incur for cgroups that do not care about kernel
>> accounting. This is why I thought it was reasonable that the kmem accounting
>> not be global.
> 
> But that happens only when pages enter and leave slab and if it still
> is significant, we can try to further optimize charging.  Given that
> this is only for cases where memcg is already in use and we provide a
> switch to disable it globally, I really don't think this warrants
> implementing fully hierarchy configuration.
> 

Not totally true. We still have to match every allocation to the right
cache, and that is actually our heaviest hit, responsible for the 2, 3 %
we're seeing when this is enabled. It is the kind of path so hot that
people frown upon branches being added, so I don't think we'll ever get
this close to being free.

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Glauber.

On Thu, Sep 27, 2012 at 10:30:36PM +0400, Glauber Costa wrote:
> > But that happens only when pages enter and leave slab and if it still
> > is significant, we can try to further optimize charging.  Given that
> > this is only for cases where memcg is already in use and we provide a
> > switch to disable it globally, I really don't think this warrants
> > implementing fully hierarchy configuration.
> 
> Not totally true. We still have to match every allocation to the right
> cache, and that is actually our heaviest hit, responsible for the 2, 3 %
> we're seeing when this is enabled. It is the kind of path so hot that
> people frown upon branches being added, so I don't think we'll ever get
> this close to being free.

Sure, depening on workload, any addition to alloc/free could be
noticeable.  I don't know.  I'll write more about it when replying to
Michal's message.  BTW, __memcg_kmem_get_cache() does seem a bit
heavy.  I wonder whether indexing from cache side would make it
cheaper?  e.g. something like the following.

	kmem_cache *__memcg_kmem_get_cache(cachep, gfp)
	{
		struct kmem_cache *c;

		c = cachep->memcg_params->caches[percpu_read(kmemcg_slab_idx)];
		if (likely(c))
			return c;
		/* try to create and then fall back to cachep */
	}

where kmemcg_slab_idx is updated from sched notifier (or maybe add and
use current->kmemcg_slab_idx?).  You would still need __GFP_* and
in_interrupt() tests but current->mm and PF_KTHREAD tests can be
rolled into index selection.

Thanks.

-- 
tejun

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/30/2012 12:23 PM, Tejun Heo wrote:
> Hello, Glauber.
> 
> On Thu, Sep 27, 2012 at 10:30:36PM +0400, Glauber Costa wrote:
>>> But that happens only when pages enter and leave slab and if it still
>>> is significant, we can try to further optimize charging.  Given that
>>> this is only for cases where memcg is already in use and we provide a
>>> switch to disable it globally, I really don't think this warrants
>>> implementing fully hierarchy configuration.
>>
>> Not totally true. We still have to match every allocation to the right
>> cache, and that is actually our heaviest hit, responsible for the 2, 3 %
>> we're seeing when this is enabled. It is the kind of path so hot that
>> people frown upon branches being added, so I don't think we'll ever get
>> this close to being free.
> 
> Sure, depening on workload, any addition to alloc/free could be
> noticeable.  I don't know.  I'll write more about it when replying to
> Michal's message.  BTW, __memcg_kmem_get_cache() does seem a bit
> heavy.  I wonder whether indexing from cache side would make it
> cheaper?  e.g. something like the following.
> 
> 	kmem_cache *__memcg_kmem_get_cache(cachep, gfp)
> 	{
> 		struct kmem_cache *c;
> 
> 		c = cachep->memcg_params->caches[percpu_read(kmemcg_slab_idx)];
> 		if (likely(c))
> 			return c;
> 		/* try to create and then fall back to cachep */
> 	}
> 
> where kmemcg_slab_idx is updated from sched notifier (or maybe add and
> use current->kmemcg_slab_idx?).  You would still need __GFP_* and
> in_interrupt() tests but current->mm and PF_KTHREAD tests can be
> rolled into index selection.
> 

How big would this array be? there can be a lot more kmem_caches than
there are memcgs. That is why it is done from memcg side.

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Glauber.

On Mon, Oct 01, 2012 at 12:45:11PM +0400, Glauber Costa wrote:
> > where kmemcg_slab_idx is updated from sched notifier (or maybe add and
> > use current->kmemcg_slab_idx?).  You would still need __GFP_* and
> > in_interrupt() tests but current->mm and PF_KTHREAD tests can be
> > rolled into index selection.
> 
> How big would this array be? there can be a lot more kmem_caches than
> there are memcgs. That is why it is done from memcg side.

The total number of memcgs are pretty limited due to the ID thing,
right?  And kmemcg is only applied to subset of caches.  I don't think
the array size would be a problem in terms of memory overhead, would
it?  If so, RCU synchronize and dynamically grow them?

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 10/04/2012 02:54 AM, Tejun Heo wrote:
> Hello, Glauber.
> 
> On Mon, Oct 01, 2012 at 12:45:11PM +0400, Glauber Costa wrote:
>>> where kmemcg_slab_idx is updated from sched notifier (or maybe add and
>>> use current->kmemcg_slab_idx?).  You would still need __GFP_* and
>>> in_interrupt() tests but current->mm and PF_KTHREAD tests can be
>>> rolled into index selection.
>>
>> How big would this array be? there can be a lot more kmem_caches than
>> there are memcgs. That is why it is done from memcg side.
> 
> The total number of memcgs are pretty limited due to the ID thing,
> right?  And kmemcg is only applied to subset of caches.  I don't think
> the array size would be a problem in terms of memory overhead, would
> it?  If so, RCU synchronize and dynamically grow them?
> 
> Thanks.
> 

I don't want to assume the number of memcgs will always be that limited.
Sure, the ID limitation sounds pretty much a big one, but people doing
VMs usually want to stack as many VMs as they possibly can in an
environment, and the less things preventing that from happening, the better.

That said, now that I've experimented with this a bit, indexing from the
cache may have some advantages: it can get too complicated to propagate
new caches appearing to all memcgs that already in-flight. We don't have
this problem from the cache side, because instances of it are guaranteed
not to exist at this point by definition.

I don't want to bloat unrelated kmem_cache structures, so I can't embed
a memcg array in there: I would have to have a pointer to a memcg array
that gets assigned at first use. But if we don't want to have a static
number, as you and christoph already frowned upon heavily, we may have
to do that memcg side as well.

The array gets bigger, though, because it pretty much has to be enough
to accomodate all css_ids. Even now, they are more than the 400 I used
in this patchset. Not allocating all of them at once will lead to more
complication and pointer chasing in here.

I'll take a look at the alternatives today and tomorrow.

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Glauber.

On Thu, Oct 04, 2012 at 03:55:14PM +0400, Glauber Costa wrote:
> I don't want to bloat unrelated kmem_cache structures, so I can't embed
> a memcg array in there: I would have to have a pointer to a memcg array
> that gets assigned at first use. But if we don't want to have a static
> number, as you and christoph already frowned upon heavily, we may have
> to do that memcg side as well.
> 
> The array gets bigger, though, because it pretty much has to be enough
> to accomodate all css_ids. Even now, they are more than the 400 I used
> in this patchset. Not allocating all of them at once will lead to more
> complication and pointer chasing in here.

I don't think it would require more pointer chasing.  At the simplest,
we can just compare the array size each time.  If you wanna be more
efficient, all arrays can be kept at the same size and resized when
the number of memcgs cross the current number.  The only runtime
overhead would be one pointer deref which I don't think can be avoided
regardless of the indexing direction.

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Michal Hocko]

On Thu 27-09-12 07:33:00, Tejun Heo wrote:
> Hello, Michal.
> 
> On Thu, Sep 27, 2012 at 02:08:06PM +0200, Michal Hocko wrote:
> > Yes, because we have many users (basically almost all) who care only
> > about the user memory because that's what occupies the vast majority of
> > the memory. They usually want to isolate workload which would disrupt
> > the global memory otherwise (e.g. backup process vs. database). You
> > really do not want to pay an additional overhead for kmem accounting
> > here.
> 
> I'm not too convinced.  First of all, the overhead added by kmemcg
> isn't big. 

You are probably talking about memory overhead which is indeed not that
big (except for possible side effects as fragmentation which you mention
bellow). But the runtime overhead is present, as far as I understand from
what Glauber said. But, on the other hand, it is fair to say that those
who _want_ use the feature should pay for it.

> The hot path overhead is quite minimal - it doesn't do much more than
> indirecting one more time.  In terms of memory usage, it sure could
> lead to a bit more fragmentation but even if it gets to several megs
> per cgroup, I don't think that's something excessive.  So, there is
> overhead but I don't believe it to be prohibitive.

Remember that users do not want to pay even "something minimal" when the
feature is not needed.

> > > So your question for global vs local switch (that again, doesn't
> > > exist; only a local *limit* exists) should really be posed in the
> > > following way:  "Can two different use cases with different needs be
> > > hosted in the same box?"
> > 
> > I think this is a good and a relevant question. I think this boils down
> > to whether you want to have trusted and untrusted workloads at the same
> > machine.
> > Trusted loads usually only need user memory accounting because kmem
> > consumption should be really negligible (unless kernel is doing
> > something really stupid and no kmem limit will help here). 
> > On the other hand, untrusted workloads can do nasty things that
> > administrator has hard time to mitigate and setting a kmem limit can
> > help significantly.
> > 
> > IMHO such a different loads exist on a single machine quite often (Web
> > server and a back up process as the most simplistic one). The per
> > hierarchy accounting, therefore, sounds like a good idea without too
> > much added complexity (actually the only added complexity is in the
> > proper kmem.limit_in_bytes handling which is a single place).
> 
> The distinction between "trusted" and "untrusted" is something
> artificially created due to the assumed deficiency of kmemcg
> implementation.  

Not really. It doesn't have to do anything with the overhead (be it
memory or runtime). It really boils down to "do I need/want it at all".
Why would I want to think about how much kernel memory is in use in the
first place? Or do you think that user memory accounting should be
deprecated?

> Making things like this visible to userland is a bad
> idea because it locks us into a place where we can't or don't need to
> improve the said deficiencies and end up pushing the difficult
> problems to somewhere else where it will likely be implemented in a
> shabbier way.  There sure are cases when such approach simply cannot
> be avoided, but I really don't think that's the case here - the
> overhead already seems to be at an acceptable level and we're not
> taking away the escape switch.
> 
> This is userland visible API.  

I am not sure which API visible part you have in mind but
kmem.limit_in_bytes will be there whether we go with global knob or "no
limit no accounting" approach. 

> We better err on the side of being conservative than going overboard
> with flexibility.  Even if we eventually need to make this switching
> fullly hierarchical, we really should be doing,
> 
> 1. Implement simple global switching and look for problem cases.
> 
> 2. Analyze them and see whether the problem case can't be solved in a
>    better, more intelligent way.
> 
> 3. If the problem is something structurally inherent or reasonably too
>    difficult to solve any other way, consider dumping the problem as
>    config parameters to userland.
> 
> We can always expand the flexibility.  Let's do the simple thing
> first.  As an added bonus, it would enable using static_keys for
> accounting branches too.

While I do agree with you in general and being careful is at place in
this area as time shown several times, this seems to be too restrictive
in this particular case.
We won't save almost no code with the global knob so I am not sure
what we are actually saving here. Global knob will just give us all or
nothing semantic without making the whole thing simpler. You will stick
with static branches and checkes whether the group accountable anyway,
right?
-- 
Michal Hocko
SUSE Labs

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hello, Michal.

On Thu, Sep 27, 2012 at 05:09:50PM +0200, Michal Hocko wrote:
> On Thu 27-09-12 07:33:00, Tejun Heo wrote:
> > I'm not too convinced.  First of all, the overhead added by kmemcg
> > isn't big. 
> 
> You are probably talking about memory overhead which is indeed not that
> big (except for possible side effects as fragmentation which you mention
> bellow). But the runtime overhead is present, as far as I understand from
> what Glauber said. But, on the other hand, it is fair to say that those
> who _want_ use the feature should pay for it.

Yeah, as long as the overhead is reasonable and it doesn't affect
non-users, I think we should put more emphasis on simplicity.  cgroup
is pretty hairy (from both implementation and interface POVs) to begin
with.  Unfortunately, what's reasonable or how much more emphasis
varies widely depending on who one asks.

> > The hot path overhead is quite minimal - it doesn't do much more than
> > indirecting one more time.  In terms of memory usage, it sure could
> > lead to a bit more fragmentation but even if it gets to several megs
> > per cgroup, I don't think that's something excessive.  So, there is
> > overhead but I don't believe it to be prohibitive.
> 
> Remember that users do not want to pay even "something minimal" when the
> feature is not needed.

Yeah but, if we can get it down to, say, around 1% under most
workloads for memcg users, it is quite questionable to introduce full
hierarchical configuration to allow avoiding that, isn't it?

> > The distinction between "trusted" and "untrusted" is something
> > artificially created due to the assumed deficiency of kmemcg
> > implementation.  
> 
> Not really. It doesn't have to do anything with the overhead (be it
> memory or runtime). It really boils down to "do I need/want it at all".
> Why would I want to think about how much kernel memory is in use in the
> first place? Or do you think that user memory accounting should be
> deprecated?

But you can apply the same "do I need/want it at all" question to the
configuration parameter too.  I can see your point but the decision
seems muddy to me, and if muddy, I prefer to err on the side of being
too conservative.

> > This is userland visible API.  
> 
> I am not sure which API visible part you have in mind but
> kmem.limit_in_bytes will be there whether we go with global knob or "no
> limit no accounting" approach. 

I mean full hierarchical configuration of it.  It becomes something
which each memcg user cares about instead of something which the base
system / admin flips on system boot.

> > We can always expand the flexibility.  Let's do the simple thing
> > first.  As an added bonus, it would enable using static_keys for
> > accounting branches too.
> 
> While I do agree with you in general and being careful is at place in
> this area as time shown several times, this seems to be too restrictive
> in this particular case.
> We won't save almost no code with the global knob so I am not sure
> what we are actually saving here. Global knob will just give us all or
> nothing semantic without making the whole thing simpler. You will stick
> with static branches and checkes whether the group accountable anyway,
> right?

The thing is about the same argument can be made about .use_hierarchy
too.  It doesn't necessarily make the code much harier.  Especially
because the code is structured with that feature on mind, removing
.use_hierarchy might not remove whole lot of code; however, the wider
range of behavior which got exposed through that poses a much larger
problem when we try to make modifications on related behaviors.  We
get a lot more locked down by seemingly not too much code and our long
term maintainability / sustainability suffers as a result.

I'm not trying to say this is as bad as .use_hierarchy but want to
point out that memcg and cgroup in general have had pretty strong
tendency to choose overly flexible and complex designs and interfaces
and it's probably about time we become more careful especially about
stuff which is visible to userland.

Thanks.

-- 
tejun

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Michal Hocko]

Hi,

On Sun 30-09-12 17:47:50, Tejun Heo wrote:
[...]
> > > The hot path overhead is quite minimal - it doesn't do much more than
> > > indirecting one more time.  In terms of memory usage, it sure could
> > > lead to a bit more fragmentation but even if it gets to several megs
> > > per cgroup, I don't think that's something excessive.  So, there is
> > > overhead but I don't believe it to be prohibitive.
> > 
> > Remember that users do not want to pay even "something minimal" when the
> > feature is not needed.
> 
> Yeah but, if we can get it down to, say, around 1% under most
> workloads for memcg users, it is quite questionable to introduce full
> hierarchical configuration to allow avoiding that, isn't it?

Remember that the kmem memory is still accounted to u+k if it is enabled
which could be a no-go because some workloads (I have provided an
example that those which are trusted are generally safe to ignore kernel
memory overhead) simply don't want to consider additional memory which
is mostly invisible for them.

> > > The distinction between "trusted" and "untrusted" is something
> > > artificially created due to the assumed deficiency of kmemcg
> > > implementation.  
> > 
> > Not really. It doesn't have to do anything with the overhead (be it
> > memory or runtime). It really boils down to "do I need/want it at all".
> > Why would I want to think about how much kernel memory is in use in the
> > first place? Or do you think that user memory accounting should be
> > deprecated?
> 
> But you can apply the same "do I need/want it at all" question to the
> configuration parameter too.  

Yes but, as I've said, the global configuration parameter is too
coarse. You can have a mix of trusted and untrusted workloads at the
same machine (e.g. web server which is inherently untrusted) and trusted
(local batch jobs which just needs a special LRU aging).

> I can see your point but the decision seems muddy to me, and if muddy,
> I prefer to err on the side of being too conservative.
> 
> > > This is userland visible API.  
> > 
> > I am not sure which API visible part you have in mind but
> > kmem.limit_in_bytes will be there whether we go with global knob or "no
> > limit no accounting" approach. 
> 
> I mean full hierarchical configuration of it.  It becomes something
> which each memcg user cares about instead of something which the base
> system / admin flips on system boot.
> 
> > > We can always expand the flexibility.  Let's do the simple thing
> > > first.  As an added bonus, it would enable using static_keys for
> > > accounting branches too.
> > 
> > While I do agree with you in general and being careful is at place in
> > this area as time shown several times, this seems to be too restrictive
> > in this particular case.
> > We won't save almost no code with the global knob so I am not sure
> > what we are actually saving here. Global knob will just give us all or
> > nothing semantic without making the whole thing simpler. You will stick
> > with static branches and checkes whether the group accountable anyway,
> > right?
> 
> The thing is about the same argument can be made about .use_hierarchy
> too.  It doesn't necessarily make the code much harier.  Especially
> because the code is structured with that feature on mind, removing
> .use_hierarchy might not remove whole lot of code; however, the wider
> range of behavior which got exposed through that poses a much larger
> problem when we try to make modifications on related behaviors.  We
> get a lot more locked down by seemingly not too much code and our long
> term maintainability / sustainability suffers as a result.

I think that comparing kmem accounting with use_hierarchy is not fair.
Glauber tried to explain why already so I will not repeat it here.
I will just mention one thing. use_hierarchy has been introduces becuase
hierarchies were expensive at the time. kmem accounting is about should
we do u or u+k accounting. So there is a crucial difference.
 
> I'm not trying to say this is as bad as .use_hierarchy but want to
> point out that memcg and cgroup in general have had pretty strong
> tendency to choose overly flexible and complex designs and interfaces
> and it's probably about time we become more careful especially about
> stuff which is visible to userland.

That is right but I think that the current discussion shows that a mixed
(kmem disabled and kmem enabled hierarchies) workloads are far from
being theoretical and a global knob is just too coarse. I am afraid we
will see "we want that per hierarchy" requests shortly and that would
just add a new confusion where global knob would complicate it
considerably (do we really want on/off/per_hierarchy global knob?).
-- 
Michal Hocko
SUSE Labs

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Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Tejun Heo]

Hey, Michal.

On Mon, Oct 01, 2012 at 11:27:56AM +0200, Michal Hocko wrote:
> > Yeah but, if we can get it down to, say, around 1% under most
> > workloads for memcg users, it is quite questionable to introduce full
> > hierarchical configuration to allow avoiding that, isn't it?
> 
> Remember that the kmem memory is still accounted to u+k if it is enabled
> which could be a no-go because some workloads (I have provided an
> example that those which are trusted are generally safe to ignore kernel
> memory overhead) simply don't want to consider additional memory which
> is mostly invisible for them.

Maybe it's because my exposure to cgroup usage is different from yours
but the argument that not accounting kernel memory is something
inherently beneficial is lost on me.  For compatibility, overhead
and/or implementation complexity issues, yeah, sure, we can't always
(well more like usually) have all we want but I don't get how not
accounting kernel memory is something inherently necessary or
beneficial.  This is all about provisioning physical memory to
different groups of users and memory is memory (that's why u+k makes
sense, right?).  Without kmemcg enabled, we not only lack a way to
control kernel memory usage but also a way to even watch per-group
usages.

> > But you can apply the same "do I need/want it at all" question to the
> > configuration parameter too.  
> 
> Yes but, as I've said, the global configuration parameter is too
> coarse. You can have a mix of trusted and untrusted workloads at the
> same machine (e.g. web server which is inherently untrusted) and trusted
> (local batch jobs which just needs a special LRU aging).

This too stems from the same difference stated above.  You think
there's inherent distinction between trusted and untrusted workloads
and they need different features from the kernel while I think why
trust anyone if you can untrust everyone and consider the knob as a
compatibility thing.

> I think that comparing kmem accounting with use_hierarchy is not fair.
> Glauber tried to explain why already so I will not repeat it here.
> I will just mention one thing. use_hierarchy has been introduces becuase
> hierarchies were expensive at the time. kmem accounting is about should
> we do u or u+k accounting. So there is a crucial difference.

It may be less crazy but I think there are enough commonalities to at
least make a comparison.  Mel seems to think it's mostly about
performance overhead.  You think that not accounting kmem is something
inherently necessary.

> That is right but I think that the current discussion shows that a mixed
> (kmem disabled and kmem enabled hierarchies) workloads are far from
> being theoretical and a global knob is just too coarse. I am afraid we

I'm not sure there's much evidence in this thread.  The strongest upto
this point seems to be performance overhead / difficulty of general
enough implementation.  As for "trusted" workload, what are the
inherent benefits of trusting if you don't have to?

> will see "we want that per hierarchy" requests shortly and that would
> just add a new confusion where global knob would complicate it
> considerably (do we really want on/off/per_hierarchy global knob?).

Hmmm?  The global knob is just the same per_hierarchy knob at the
root.  It's hierarchical after all.

Anyways, as long as the "we silently ignore what happened before being
enabled" is gone, I won't fight this anymore.  It isn't broken after
all.  But, please think about making things simpler in general, cgroup
is riddled with mis-designed complexities and memcg seems to be
leading the charge at times.

Thanks.

-- 
tejun

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Michal Hocko]

On Thu 04-10-12 07:43:16, Tejun Heo wrote:
[...]
> > That is right but I think that the current discussion shows that a mixed
> > (kmem disabled and kmem enabled hierarchies) workloads are far from
> > being theoretical and a global knob is just too coarse. I am afraid we
> 
> I'm not sure there's much evidence in this thread.  The strongest upto
> this point seems to be performance overhead / difficulty of general
> enough implementation.  As for "trusted" workload, what are the
> inherent benefits of trusting if you don't have to?

One advantage is that you do _not have_ to consider kernel memory
allocations (which are inherently bound to the kernel version) so the
sizing is much easier and version independent. If you set a limit to XY
because you know what you are doing you certainly do not want to regress
(e.g. because of unnecessary reclaim) just because a certain kernel
allocation got bigger, right?

> > will see "we want that per hierarchy" requests shortly and that would
> > just add a new confusion where global knob would complicate it
> > considerably (do we really want on/off/per_hierarchy global knob?).
> 
> Hmmm?  The global knob is just the same per_hierarchy knob at the
> root.  It's hierarchical after all.

When you said global knob I imagined mount or boot option. If you want
to have yet another memory.enable_kmem then IMHO it is much easier to
use set-accounted semantic (which is hierarchical as well).

> Anyways, as long as the "we silently ignore what happened before being
> enabled" is gone, I won't fight this anymore.  It isn't broken after
> all.  

OK, it is good that we settled this.

> But, please think about making things simpler in general, cgroup
> is riddled with mis-designed complexities and memcg seems to be
> leading the charge at times.

Yes this is an evolution and it seems that we are slowly getting there.

> 
> Thanks.

-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Johannes Weiner]

On Thu, Sep 27, 2012 at 12:02:14AM +0400, Glauber Costa wrote:
> On 09/26/2012 11:56 PM, Tejun Heo wrote:
> > Hello,
> > 
> > On Wed, Sep 26, 2012 at 11:46:37PM +0400, Glauber Costa wrote:
> >> Besides not being part of cgroup core, and respecting very much both
> >> cgroups' and basic sanity properties, kmem is an actual feature that
> >> some people want, and some people don't. There is no reason to believe
> >> that applications that want will live in the same environment with ones
> >> that don't want.
> > 
> > I don't know.  It definitely is less crazy than .use_hierarchy but I
> > wouldn't say it's an inherently different thing.  I mean, what does it
> > even mean to have u+k limit on one subtree and not on another branch?
> > And we worry about things like what if parent doesn't enable it but
> > its chlidren do.
> > 
> 
> It is inherently different. To begin with, it actually contemplates two
> use cases. It is not a work around.
> 
> The meaning is also very well defined. The meaning of having this
> enabled in one subtree and not in other is: Subtree A wants to track
> kernel memory. Subtree B does not. It's that, and never more than that.
> There is no maybes and no buts, no magic knobs that makes it behave in a
> crazy way.
> 
> If a children enables it but the parent does not, this does what every
> tree does: enable it from that point downwards.
> 
> > This is a feature which adds complexity.  If the feature is necessary
> > and justified, sure.  If not, let's please not and let's err on the
> > side of conservativeness.  We can always add it later but the other
> > direction is much harder.
> 
> I disagree. Having kmem tracking adds complexity. Having to cope with
> the use case where we turn it on dynamically to cope with the "user page
> only" use case adds complexity. But I see no significant complexity
> being added by having it per subtree. Really.

Maybe not in code, but you are adding an extra variable into the
system.  "One switch per subtree" is more complex than "one switch."
Yes, the toggle is hidden behind setting the limit, but it's still a
toggle.  The use_hierarchy complexity comes not from the file that
enables it, but from the resulting semantics.

kmem accounting is expensive and we definitely want to allow enabling
it separately from traditional user memory accounting.  But I think
there is no good reason to not demand an all-or-nothing answer from
the admin; either he wants kmem tracking on a machine or not.  At
least you haven't presented a convincing case, IMO.

I don't think there is strong/any demand for per-node toggles, but
once we add this behavior, people will rely on it and expect kmem
tracking to stay local and we are stuck with it.  Adding it for the
reason that people will use it is a self-fulfilling prophecy.

> You have the use_hierarchy fiasco in mind, and I do understand that you
> are raising the flag and all that.
> 
> But think in terms of functionality: This thing here is a lot more
> similar to swap than use_hierarchy. Would you argue that memsw should be
> per-root ?

We actually do have a per-root flag that controls accounting for swap.

> The reason why it shouldn't: Some people want to limit memory
> consumption all the way to the swap, some people don't. Same with kmem.

That lies in the nature of the interface: we chose k & u+k rather than
u & u+k, so our memory.limit_in_bytes will necessarily include kmem,
while swap is not included there.  But I really doubt that there is a
strong case for turning on swap accounting intentionally and then
limiting memory+swap only on certain subtrees.  Where would be the
sense in that?

Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/27/2012 02:11 AM, Johannes Weiner wrote:
> On Thu, Sep 27, 2012 at 12:02:14AM +0400, Glauber Costa wrote:
>> On 09/26/2012 11:56 PM, Tejun Heo wrote:
>>> Hello,
>>>
>>> On Wed, Sep 26, 2012 at 11:46:37PM +0400, Glauber Costa wrote:
>>>> Besides not being part of cgroup core, and respecting very much both
>>>> cgroups' and basic sanity properties, kmem is an actual feature that
>>>> some people want, and some people don't. There is no reason to believe
>>>> that applications that want will live in the same environment with ones
>>>> that don't want.
>>>
>>> I don't know.  It definitely is less crazy than .use_hierarchy but I
>>> wouldn't say it's an inherently different thing.  I mean, what does it
>>> even mean to have u+k limit on one subtree and not on another branch?
>>> And we worry about things like what if parent doesn't enable it but
>>> its chlidren do.
>>>
>>
>> It is inherently different. To begin with, it actually contemplates two
>> use cases. It is not a work around.
>>
>> The meaning is also very well defined. The meaning of having this
>> enabled in one subtree and not in other is: Subtree A wants to track
>> kernel memory. Subtree B does not. It's that, and never more than that.
>> There is no maybes and no buts, no magic knobs that makes it behave in a
>> crazy way.
>>
>> If a children enables it but the parent does not, this does what every
>> tree does: enable it from that point downwards.
>>
>>> This is a feature which adds complexity.  If the feature is necessary
>>> and justified, sure.  If not, let's please not and let's err on the
>>> side of conservativeness.  We can always add it later but the other
>>> direction is much harder.
>>
>> I disagree. Having kmem tracking adds complexity. Having to cope with
>> the use case where we turn it on dynamically to cope with the "user page
>> only" use case adds complexity. But I see no significant complexity
>> being added by having it per subtree. Really.
> 
> Maybe not in code, but you are adding an extra variable into the
> system.  "One switch per subtree" is more complex than "one switch."
> Yes, the toggle is hidden behind setting the limit, but it's still a
> toggle.  The use_hierarchy complexity comes not from the file that
> enables it, but from the resulting semantics.
> 

I didn't claim the complexity was in the code. I actually think the
other way around that you do, and claim that a global switch is more
complex than a per-subtree. All properties we have so far applies to
subtrees, due to cgroup's hierarchical nature. We have no global
switches like this so far, and adding one would just add a new concept
that wasn't here.


> kmem accounting is expensive and we definitely want to allow enabling
> it separately from traditional user memory accounting.  But I think
> there is no good reason to not demand an all-or-nothing answer from
> the admin; either he wants kmem tracking on a machine or not.  At
> least you haven't presented a convincing case, IMO.
> 
> I don't think there is strong/any demand for per-node toggles, but
> once we add this behavior, people will rely on it and expect kmem
> tracking to stay local and we are stuck with it.  Adding it for the
> reason that people will use it is a self-fulfilling prophecy.


I don't think this is a compatibility only switch. Much has been said in
the past about the problem of sharing. A lot of the kernel objects are
shared by nature, this is pretty much unavoidable. The answer we have
been giving to this inquiry, is that the workloads (us) interested
in kmem accounted tend to be quite local in their file accesses (and
other kernel objects as well).

It should be obvious that not all workloads are like this, and some of
them would actually prefer to have their umem limited only.

I really don't think, and correct me if I am wrong, that the problem
lays in "is there a use case for umem?", but rather, if they should be
allowed to coexist in a box.

And honestly, it seems to me totally reasonable to avoid restricting
people to run as many workloads they think they can in the same box.


>> You have the use_hierarchy fiasco in mind, and I do understand that you
>> are raising the flag and all that.
>>
>> But think in terms of functionality: This thing here is a lot more
>> similar to swap than use_hierarchy. Would you argue that memsw should be
>> per-root ?
> 
> We actually do have a per-root flag that controls accounting for swap.
> 
>> The reason why it shouldn't: Some people want to limit memory
>> consumption all the way to the swap, some people don't. Same with kmem.
> 
> That lies in the nature of the interface: we chose k & u+k rather than
> u & u+k, so our memory.limit_in_bytes will necessarily include kmem,
> while swap is not included there.  But I really doubt that there is a
> strong case for turning on swap accounting intentionally and then
> limiting memory+swap only on certain subtrees.  Where would be the
> sense in that?

It makes absolute sense. Because until I go set
memory.memsw.limit_in_bytes, my subtree is not limited, which is
precisely what kmem does.

And the use cases for that are:

1) I, application A, want to use 2G of mem, and I can never swap
2) I, application B, want to use 2G of mem, but I am fine using extra 1G
in swap.

There are plenty of workloads in both the "can swap" and "can't swap"
category around.

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[PATCH v3 05/13] Add a __GFP_KMEMCG flag

[Glauber Costa]

This flag is used to indicate to the callees that this allocation is a
kernel allocation in process context, and should be accounted to
current's memcg. It takes numerical place of the of the recently removed
__GFP_NO_KSWAPD.

Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
CC: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
CC: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
CC: Rik van Riel <riel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
CC: Mel Gorman <mel-wPRd99KPJ+uzQB+pC5nmwQ@public.gmane.org>
Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
---
 include/linux/gfp.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index f9bc873..d8eae4d 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -35,6 +35,11 @@ struct vm_area_struct;
 #else
 #define ___GFP_NOTRACK		0
 #endif
+#ifdef CONFIG_MEMCG_KMEM
+#define ___GFP_KMEMCG		0x400000u
+#else
+#define ___GFP_KMEMCG		0
+#endif
 #define ___GFP_OTHER_NODE	0x800000u
 #define ___GFP_WRITE		0x1000000u
 
@@ -91,7 +96,7 @@ struct vm_area_struct;
 
 #define __GFP_OTHER_NODE ((__force gfp_t)___GFP_OTHER_NODE) /* On behalf of other node */
 #define __GFP_WRITE	((__force gfp_t)___GFP_WRITE)	/* Allocator intends to dirty page */
-
+#define __GFP_KMEMCG	((__force gfp_t)___GFP_KMEMCG) /* Allocation comes from a memcg-accounted resource */
 /*
  * This may seem redundant, but it's a way of annotating false positives vs.
  * allocations that simply cannot be supported (e.g. page tables).
-- 
1.7.11.4

Re: [PATCH v3 05/13] Add a __GFP_KMEMCG flag

[Rik van Riel]

On 09/18/2012 10:04 AM, Glauber Costa wrote:
> This flag is used to indicate to the callees that this allocation is a
> kernel allocation in process context, and should be accounted to
> current's memcg. It takes numerical place of the of the recently removed
> __GFP_NO_KSWAPD.
>
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> CC: Christoph Lameter <cl@linux.com>
> CC: Pekka Enberg <penberg@cs.helsinki.fi>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Suleiman Souhlal <suleiman@google.com>
> CC: Rik van Riel <riel@redhat.com>
> CC: Mel Gorman <mel@csn.ul.ie>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Acked-by: Rik van Riel <riel@redhat.com>


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Re: [PATCH v3 05/13] Add a __GFP_KMEMCG flag

[Christoph Lameter]

On Tue, 18 Sep 2012, Glauber Costa wrote:

> +++ b/include/linux/gfp.h
> @@ -35,6 +35,11 @@ struct vm_area_struct;
>  #else
>  #define ___GFP_NOTRACK		0
>  #endif
> +#ifdef CONFIG_MEMCG_KMEM
> +#define ___GFP_KMEMCG		0x400000u
> +#else
> +#define ___GFP_KMEMCG		0
> +#endif

Could you leave __GFP_MEMCG a simple definition and then define GFP_MEMCG
to be zer0 if !MEMCG_KMEM? I think that would be cleaner and the
__GFP_KMEMCHECK another case that would be good to fix up.

Re: [PATCH v3 05/13] Add a __GFP_KMEMCG flag

[Glauber Costa]

On 09/18/2012 07:06 PM, Christoph Lameter wrote:
> On Tue, 18 Sep 2012, Glauber Costa wrote:
> 
>> +++ b/include/linux/gfp.h
>> @@ -35,6 +35,11 @@ struct vm_area_struct;
>>  #else
>>  #define ___GFP_NOTRACK		0
>>  #endif
>> +#ifdef CONFIG_MEMCG_KMEM
>> +#define ___GFP_KMEMCG		0x400000u
>> +#else
>> +#define ___GFP_KMEMCG		0
>> +#endif
> 
> Could you leave __GFP_MEMCG a simple definition and then define GFP_MEMCG
> to be zer0 if !MEMCG_KMEM? I think that would be cleaner and the
> __GFP_KMEMCHECK another case that would be good to fix up.
> 
> 
> 
I can, but what does this buy us?
Also, in any case, this can be done incrementally, and for the other
flag as well, as you describe.

Re: [PATCH v3 05/13] Add a __GFP_KMEMCG flag

[Christoph Lameter]

On Wed, 19 Sep 2012, Glauber Costa wrote:

> On 09/18/2012 07:06 PM, Christoph Lameter wrote:
> > On Tue, 18 Sep 2012, Glauber Costa wrote:
> >
> >> +++ b/include/linux/gfp.h
> >> @@ -35,6 +35,11 @@ struct vm_area_struct;
> >>  #else
> >>  #define ___GFP_NOTRACK		0
> >>  #endif
> >> +#ifdef CONFIG_MEMCG_KMEM
> >> +#define ___GFP_KMEMCG		0x400000u
> >> +#else
> >> +#define ___GFP_KMEMCG		0
> >> +#endif
> >
> > Could you leave __GFP_MEMCG a simple definition and then define GFP_MEMCG
> > to be zer0 if !MEMCG_KMEM? I think that would be cleaner and the
> > __GFP_KMEMCHECK another case that would be good to fix up.
> >
> >
> >
> I can, but what does this buy us?

All the numeric values should be defined with __ unconditionally so that
they can be used in future context. Note the comment above the __GFP_XX
which says "Do not use this directly".

> Also, in any case, this can be done incrementally, and for the other
> flag as well, as you describe.

There is only one other flag that does not follow the scheme. I'd
appreciate it if you could submit a patch to fix up the __GFP_NOTRACK
conditional there.

There is no need to do this incrementally. Do it the right way
immediately.

Re: [PATCH v3 05/13] Add a __GFP_KMEMCG flag

[Mel Gorman]

On Tue, Sep 18, 2012 at 06:04:02PM +0400, Glauber Costa wrote:
> This flag is used to indicate to the callees that this allocation is a
> kernel allocation in process context, and should be accounted to
> current's memcg. It takes numerical place of the of the recently removed
> __GFP_NO_KSWAPD.
> 
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> CC: Christoph Lameter <cl@linux.com>
> CC: Pekka Enberg <penberg@cs.helsinki.fi>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Suleiman Souhlal <suleiman@google.com>
> CC: Rik van Riel <riel@redhat.com>
> CC: Mel Gorman <mel@csn.ul.ie>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

I agree with Christophs recommendation that this flag always exist instead
of being 0 in the !MEMCG_KMEM case. If __GFP_KMEMCG ever is used in another
part of the VM (which would be unexpected but still) then the behaviour
might differ too much between MEMCG_KMEM and !MEMCG_KMEM cases. As unlikely
as the case is, it's not impossible.

For tracing __GFP_KMEMCG should have an entry in
include/trace/events/gfpflags.h

Get rid of the CONFIG_MEMCG_KMEM check and update
include/trace/events/gfpflags.h and then feel free to stick my Acked-by
on it.

-- 
Mel Gorman
SUSE Labs

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Re: [PATCH v3 05/13] Add a __GFP_KMEMCG flag

[Glauber Costa]

On 09/27/2012 05:34 PM, Mel Gorman wrote:
> On Tue, Sep 18, 2012 at 06:04:02PM +0400, Glauber Costa wrote:
>> This flag is used to indicate to the callees that this allocation is a
>> kernel allocation in process context, and should be accounted to
>> current's memcg. It takes numerical place of the of the recently removed
>> __GFP_NO_KSWAPD.
>>
>> Signed-off-by: Glauber Costa <glommer@parallels.com>
>> CC: Christoph Lameter <cl@linux.com>
>> CC: Pekka Enberg <penberg@cs.helsinki.fi>
>> CC: Michal Hocko <mhocko@suse.cz>
>> CC: Johannes Weiner <hannes@cmpxchg.org>
>> CC: Suleiman Souhlal <suleiman@google.com>
>> CC: Rik van Riel <riel@redhat.com>
>> CC: Mel Gorman <mel@csn.ul.ie>
>> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> I agree with Christophs recommendation that this flag always exist instead
> of being 0 in the !MEMCG_KMEM case. If __GFP_KMEMCG ever is used in another
> part of the VM (which would be unexpected but still) then the behaviour
> might differ too much between MEMCG_KMEM and !MEMCG_KMEM cases. As unlikely
> as the case is, it's not impossible.
> 
> For tracing __GFP_KMEMCG should have an entry in
> include/trace/events/gfpflags.h
> 
> Get rid of the CONFIG_MEMCG_KMEM check and update
> include/trace/events/gfpflags.h and then feel free to stick my Acked-by
> on it.
> 

Thanks, that is certainly doable.

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Re: [PATCH v3 05/13] Add a __GFP_KMEMCG flag

[Johannes Weiner]

On Tue, Sep 18, 2012 at 06:04:02PM +0400, Glauber Costa wrote:
> This flag is used to indicate to the callees that this allocation is a
> kernel allocation in process context, and should be accounted to
> current's memcg. It takes numerical place of the of the recently removed
> __GFP_NO_KSWAPD.
> 
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> CC: Christoph Lameter <cl@linux.com>
> CC: Pekka Enberg <penberg@cs.helsinki.fi>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Suleiman Souhlal <suleiman@google.com>
> CC: Rik van Riel <riel@redhat.com>
> CC: Mel Gorman <mel@csn.ul.ie>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

With the feedback from Christoph and Mel incorporated:

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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[PATCH v3 06/13] memcg: kmem controller infrastructure

[Glauber Costa]

This patch introduces infrastructure for tracking kernel memory pages to
a given memcg. This will happen whenever the caller includes the flag
__GFP_KMEMCG flag, and the task belong to a memcg other than the root.

In memcontrol.h those functions are wrapped in inline acessors.  The
idea is to later on, patch those with static branches, so we don't incur
any overhead when no mem cgroups with limited kmem are being used.

[ v2: improved comments and standardized function names ]
[ v3: handle no longer opaque, functions not exported,
  even more comments ]
[ v4: reworked Used bit handling and surroundings for more clarity ]

Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
CC: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
---
 include/linux/memcontrol.h |  97 +++++++++++++++++++++++++
 mm/memcontrol.c            | 177 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 274 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 8d9489f..82ede9a 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -21,6 +21,7 @@
 #define _LINUX_MEMCONTROL_H
 #include <linux/cgroup.h>
 #include <linux/vm_event_item.h>
+#include <linux/hardirq.h>
 
 struct mem_cgroup;
 struct page_cgroup;
@@ -399,6 +400,17 @@ struct sock;
 #ifdef CONFIG_MEMCG_KMEM
 void sock_update_memcg(struct sock *sk);
 void sock_release_memcg(struct sock *sk);
+
+static inline bool memcg_kmem_enabled(void)
+{
+	return true;
+}
+
+extern bool __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg,
+					int order);
+extern void __memcg_kmem_commit_charge(struct page *page,
+				       struct mem_cgroup *memcg, int order);
+extern void __memcg_kmem_uncharge_page(struct page *page, int order);
 #else
 static inline void sock_update_memcg(struct sock *sk)
 {
@@ -406,6 +418,91 @@ static inline void sock_update_memcg(struct sock *sk)
 static inline void sock_release_memcg(struct sock *sk)
 {
 }
+
+static inline bool memcg_kmem_enabled(void)
+{
+	return false;
+}
+
+static inline bool
+__memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg, int order)
+{
+	return false;
+}
+
+static inline void  __memcg_kmem_uncharge_page(struct page *page, int order)
+{
+}
+
+static inline void
+__memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg, int order)
+{
+}
 #endif /* CONFIG_MEMCG_KMEM */
+
+/**
+ * memcg_kmem_newpage_charge: verify if a new kmem allocation is allowed.
+ * @gfp: the gfp allocation flags.
+ * @memcg: a pointer to the memcg this was charged against.
+ * @order: allocation order.
+ *
+ * returns true if the memcg where the current task belongs can hold this
+ * allocation.
+ *
+ * We return true automatically if this allocation is not to be accounted to
+ * any memcg.
+ */
+static __always_inline bool
+memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg, int order)
+{
+	if (!memcg_kmem_enabled())
+		return true;
+
+	/*
+	 * __GFP_NOFAIL allocations will move on even if charging is not
+	 * possible. Therefore we don't even try, and have this allocation
+	 * unaccounted. We could in theory charge it with
+	 * res_counter_charge_nofail, but we hope those allocations are rare,
+	 * and won't be worth the trouble.
+	 */
+	if (!(gfp & __GFP_KMEMCG) || (gfp & __GFP_NOFAIL))
+		return true;
+	if (in_interrupt() || (!current->mm) || (current->flags & PF_KTHREAD))
+		return true;
+	return __memcg_kmem_newpage_charge(gfp, memcg, order);
+}
+
+/**
+ * memcg_kmem_uncharge_page: uncharge pages from memcg
+ * @page: pointer to struct page being freed
+ * @order: allocation order.
+ *
+ * there is no need to specify memcg here, since it is embedded in page_cgroup
+ */
+static __always_inline void
+memcg_kmem_uncharge_page(struct page *page, int order)
+{
+	if (memcg_kmem_enabled())
+		__memcg_kmem_uncharge_page(page, order);
+}
+
+/**
+ * memcg_kmem_commit_charge: embeds correct memcg in a page
+ * @memcg: a pointer to the memcg this was charged against.
+ * @page: pointer to struct page recently allocated
+ * @memcg: the memcg structure we charged against
+ * @order: allocation order.
+ *
+ * Needs to be called after memcg_kmem_newpage_charge, regardless of success or
+ * failure of the allocation. if @page is NULL, this function will revert the
+ * charges. Otherwise, it will commit the memcg given by @memcg to the
+ * corresponding page_cgroup.
+ */
+static __always_inline void
+memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg, int order)
+{
+	if (memcg_kmem_enabled() && memcg)
+		__memcg_kmem_commit_charge(page, memcg, order);
+}
 #endif /* _LINUX_MEMCONTROL_H */
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f3fd354..0f36a01 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -10,6 +10,10 @@
  * Copyright (C) 2009 Nokia Corporation
  * Author: Kirill A. Shutemov
  *
+ * Kernel Memory Controller
+ * Copyright (C) 2012 Parallels Inc. and Google Inc.
+ * Authors: Glauber Costa and Suleiman Souhlal
+ *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
@@ -426,6 +430,9 @@ struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
 #include <net/ip.h>
 
 static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
+static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size);
+static void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size);
+
 void sock_update_memcg(struct sock *sk)
 {
 	if (mem_cgroup_sockets_enabled) {
@@ -480,6 +487,110 @@ struct cg_proto *tcp_proto_cgroup(struct mem_cgroup *memcg)
 }
 EXPORT_SYMBOL(tcp_proto_cgroup);
 #endif /* CONFIG_INET */
+
+static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
+{
+	return !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) &&
+		memcg->kmem_accounted;
+}
+
+/*
+ * We need to verify if the allocation against current->mm->owner's memcg is
+ * possible for the given order. But the page is not allocated yet, so we'll
+ * need a further commit step to do the final arrangements.
+ *
+ * It is possible for the task to switch cgroups in this mean time, so at
+ * commit time, we can't rely on task conversion any longer.  We'll then use
+ * the handle argument to return to the caller which cgroup we should commit
+ * against. We could also return the memcg directly and avoid the pointer
+ * passing, but a boolean return value gives better semantics considering
+ * the compiled-out case as well.
+ *
+ * Returning true means the allocation is possible.
+ */
+bool
+__memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
+{
+	struct mem_cgroup *memcg;
+	bool ret;
+	struct task_struct *p;
+
+	*_memcg = NULL;
+	rcu_read_lock();
+	p = rcu_dereference(current->mm->owner);
+	memcg = mem_cgroup_from_task(p);
+	rcu_read_unlock();
+
+	if (!memcg_can_account_kmem(memcg))
+		return true;
+
+	mem_cgroup_get(memcg);
+
+	ret = memcg_charge_kmem(memcg, gfp, PAGE_SIZE << order) == 0;
+	if (ret)
+		*_memcg = memcg;
+	else
+		mem_cgroup_put(memcg);
+
+	return ret;
+}
+
+void __memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg,
+			      int order)
+{
+	struct page_cgroup *pc;
+
+	WARN_ON(mem_cgroup_is_root(memcg));
+
+	/* The page allocation failed. Revert */
+	if (!page) {
+		memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
+		return;
+	}
+
+	pc = lookup_page_cgroup(page);
+	lock_page_cgroup(pc);
+	pc->mem_cgroup = memcg;
+	SetPageCgroupUsed(pc);
+	unlock_page_cgroup(pc);
+}
+
+void __memcg_kmem_uncharge_page(struct page *page, int order)
+{
+	struct mem_cgroup *memcg = NULL;
+	struct page_cgroup *pc;
+
+
+	pc = lookup_page_cgroup(page);
+	/*
+	 * Fast unlocked return. Theoretically might have changed, have to
+	 * check again after locking.
+	 */
+	if (!PageCgroupUsed(pc))
+		return;
+
+	lock_page_cgroup(pc);
+	if (PageCgroupUsed(pc)) {
+		memcg = pc->mem_cgroup;
+		ClearPageCgroupUsed(pc);
+	}
+	unlock_page_cgroup(pc);
+
+	/*
+	 * Checking if kmem accounted is enabled won't work for uncharge, since
+	 * it is possible that the user enabled kmem tracking, allocated, and
+	 * then disabled it again.
+	 *
+	 * We trust if there is a memcg associated with the page, it is a valid
+	 * allocation
+	 */
+	if (!memcg)
+		return;
+
+	WARN_ON(mem_cgroup_is_root(memcg));
+	memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
+	mem_cgroup_put(memcg);
+}
 #endif /* CONFIG_MEMCG_KMEM */
 
 #if defined(CONFIG_INET) && defined(CONFIG_MEMCG_KMEM)
@@ -5700,3 +5811,69 @@ static int __init enable_swap_account(char *s)
 __setup("swapaccount=", enable_swap_account);
 
 #endif
+
+#ifdef CONFIG_MEMCG_KMEM
+int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size)
+{
+	struct res_counter *fail_res;
+	struct mem_cgroup *_memcg;
+	int ret;
+	bool may_oom;
+	bool nofail = false;
+
+	may_oom = (gfp & __GFP_WAIT) && (gfp & __GFP_FS) &&
+	    !(gfp & __GFP_NORETRY);
+
+	ret = 0;
+
+	if (!memcg)
+		return ret;
+
+	_memcg = memcg;
+	ret = __mem_cgroup_try_charge(NULL, gfp, size / PAGE_SIZE,
+	    &_memcg, may_oom);
+
+	if (ret == -EINTR)  {
+		nofail = true;
+		/*
+		 * __mem_cgroup_try_charge() chosed to bypass to root due to
+		 * OOM kill or fatal signal.  Since our only options are to
+		 * either fail the allocation or charge it to this cgroup, do
+		 * it as a temporary condition. But we can't fail. From a
+		 * kmem/slab perspective, the cache has already been selected,
+		 * by mem_cgroup_get_kmem_cache(), so it is too late to change
+		 * our minds
+		 */
+		res_counter_charge_nofail(&memcg->res, size, &fail_res);
+		if (do_swap_account)
+			res_counter_charge_nofail(&memcg->memsw, size,
+						  &fail_res);
+		ret = 0;
+	} else if (ret == -ENOMEM)
+		return ret;
+
+	if (nofail)
+		res_counter_charge_nofail(&memcg->kmem, size, &fail_res);
+	else
+		ret = res_counter_charge(&memcg->kmem, size, &fail_res);
+
+	if (ret) {
+		res_counter_uncharge(&memcg->res, size);
+		if (do_swap_account)
+			res_counter_uncharge(&memcg->memsw, size);
+	}
+
+	return ret;
+}
+
+void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size)
+{
+	if (!memcg)
+		return;
+
+	res_counter_uncharge(&memcg->kmem, size);
+	res_counter_uncharge(&memcg->res, size);
+	if (do_swap_account)
+		res_counter_uncharge(&memcg->memsw, size);
+}
+#endif /* CONFIG_MEMCG_KMEM */
-- 
1.7.11.4

Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[JoonSoo Kim]

Hi, Glauber.

2012/9/18 Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>:
> +/*
> + * We need to verify if the allocation against current->mm->owner's memcg is
> + * possible for the given order. But the page is not allocated yet, so we'll
> + * need a further commit step to do the final arrangements.
> + *
> + * It is possible for the task to switch cgroups in this mean time, so at
> + * commit time, we can't rely on task conversion any longer.  We'll then use
> + * the handle argument to return to the caller which cgroup we should commit
> + * against. We could also return the memcg directly and avoid the pointer
> + * passing, but a boolean return value gives better semantics considering
> + * the compiled-out case as well.
> + *
> + * Returning true means the allocation is possible.
> + */
> +bool
> +__memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
> +{
> +       struct mem_cgroup *memcg;
> +       bool ret;
> +       struct task_struct *p;
> +
> +       *_memcg = NULL;
> +       rcu_read_lock();
> +       p = rcu_dereference(current->mm->owner);
> +       memcg = mem_cgroup_from_task(p);
> +       rcu_read_unlock();
> +
> +       if (!memcg_can_account_kmem(memcg))
> +               return true;
> +
> +       mem_cgroup_get(memcg);
> +
> +       ret = memcg_charge_kmem(memcg, gfp, PAGE_SIZE << order) == 0;
> +       if (ret)
> +               *_memcg = memcg;
> +       else
> +               mem_cgroup_put(memcg);
> +
> +       return ret;
> +}

"*_memcg = memcg" should be executed when "memcg_charge_kmem" is success.
"memcg_charge_kmem" return 0 if success in charging.
Therefore, I think this code is wrong.
If I am right, it is a serious bug that affect behavior of all the patchset.

> +void __memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg,
> +                             int order)
> +{
> +       struct page_cgroup *pc;
> +
> +       WARN_ON(mem_cgroup_is_root(memcg));
> +
> +       /* The page allocation failed. Revert */
> +       if (!page) {
> +               memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
> +               return;
> +       }

In case of "!page ", mem_cgroup_put(memcg) is needed,
because we already call "mem_cgroup_get(memcg)" in
__memcg_kmem_newpage_charge().
I know that mem_cgroup_put()/get() will be removed in later patch, but
it is important that every patch works fine.

Thanks.

Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Glauber Costa]

On 09/20/2012 08:05 PM, JoonSoo Kim wrote:
> Hi, Glauber.
> 
> 2012/9/18 Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>:
>> +/*
>> + * We need to verify if the allocation against current->mm->owner's memcg is
>> + * possible for the given order. But the page is not allocated yet, so we'll
>> + * need a further commit step to do the final arrangements.
>> + *
>> + * It is possible for the task to switch cgroups in this mean time, so at
>> + * commit time, we can't rely on task conversion any longer.  We'll then use
>> + * the handle argument to return to the caller which cgroup we should commit
>> + * against. We could also return the memcg directly and avoid the pointer
>> + * passing, but a boolean return value gives better semantics considering
>> + * the compiled-out case as well.
>> + *
>> + * Returning true means the allocation is possible.
>> + */
>> +bool
>> +__memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
>> +{
>> +       struct mem_cgroup *memcg;
>> +       bool ret;
>> +       struct task_struct *p;
>> +
>> +       *_memcg = NULL;
>> +       rcu_read_lock();
>> +       p = rcu_dereference(current->mm->owner);
>> +       memcg = mem_cgroup_from_task(p);
>> +       rcu_read_unlock();
>> +
>> +       if (!memcg_can_account_kmem(memcg))
>> +               return true;
>> +
>> +       mem_cgroup_get(memcg);
>> +
>> +       ret = memcg_charge_kmem(memcg, gfp, PAGE_SIZE << order) == 0;
>> +       if (ret)
>> +               *_memcg = memcg;
>> +       else
>> +               mem_cgroup_put(memcg);
>> +
>> +       return ret;
>> +}
> 
> "*_memcg = memcg" should be executed when "memcg_charge_kmem" is success.
> "memcg_charge_kmem" return 0 if success in charging.
> Therefore, I think this code is wrong.
> If I am right, it is a serious bug that affect behavior of all the patchset.

Which is precisely what it does. ret is a boolean, that will be true
when charge succeeded (== 0 test)

> 
>> +void __memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg,
>> +                             int order)
>> +{
>> +       struct page_cgroup *pc;
>> +
>> +       WARN_ON(mem_cgroup_is_root(memcg));
>> +
>> +       /* The page allocation failed. Revert */
>> +       if (!page) {
>> +               memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
>> +               return;
>> +       }
> 
> In case of "!page ", mem_cgroup_put(memcg) is needed,
> because we already call "mem_cgroup_get(memcg)" in
> __memcg_kmem_newpage_charge().
> I know that mem_cgroup_put()/get() will be removed in later patch, but
> it is important that every patch works fine.

Okay, I'll add the put here. It is indeed missing.

Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[JoonSoo Kim]

>> "*_memcg = memcg" should be executed when "memcg_charge_kmem" is success.
>> "memcg_charge_kmem" return 0 if success in charging.
>> Therefore, I think this code is wrong.
>> If I am right, it is a serious bug that affect behavior of all the patchset.
>
> Which is precisely what it does. ret is a boolean, that will be true
> when charge succeeded (== 0 test)

Ahh...Okay! I didn't see (== 0 test)

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Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Michal Hocko]

On Tue 18-09-12 18:04:03, Glauber Costa wrote:
> This patch introduces infrastructure for tracking kernel memory pages to
> a given memcg. This will happen whenever the caller includes the flag
> __GFP_KMEMCG flag, and the task belong to a memcg other than the root.
> 
> In memcontrol.h those functions are wrapped in inline acessors.  The
> idea is to later on, patch those with static branches, so we don't incur
> any overhead when no mem cgroups with limited kmem are being used.

Could you describe the API a bit here, please? I guess the
kernel user is supposed to call memcg_kmem_newpage_charge and
memcg_kmem_commit_charge resp. memcg_kmem_uncharge_page.
All other kmem functions here are just helpers, right?
> 
> [ v2: improved comments and standardized function names ]
> [ v3: handle no longer opaque, functions not exported,
>   even more comments ]
> [ v4: reworked Used bit handling and surroundings for more clarity ]
> 
> Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
> CC: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
> CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
> CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
> CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> ---
>  include/linux/memcontrol.h |  97 +++++++++++++++++++++++++
>  mm/memcontrol.c            | 177 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 274 insertions(+)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 8d9489f..82ede9a 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -21,6 +21,7 @@
>  #define _LINUX_MEMCONTROL_H
>  #include <linux/cgroup.h>
>  #include <linux/vm_event_item.h>
> +#include <linux/hardirq.h>
>
>  struct mem_cgroup;
>  struct page_cgroup;
> @@ -399,6 +400,17 @@ struct sock;
>  #ifdef CONFIG_MEMCG_KMEM
>  void sock_update_memcg(struct sock *sk);
>  void sock_release_memcg(struct sock *sk);
> +
> +static inline bool memcg_kmem_enabled(void)
> +{
> +	return true;
> +}
> +
> +extern bool __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg,
> +					int order);
> +extern void __memcg_kmem_commit_charge(struct page *page,
> +				       struct mem_cgroup *memcg, int order);
> +extern void __memcg_kmem_uncharge_page(struct page *page, int order);
>  #else
>  static inline void sock_update_memcg(struct sock *sk)
>  {
> @@ -406,6 +418,91 @@ static inline void sock_update_memcg(struct sock *sk)
>  static inline void sock_release_memcg(struct sock *sk)
>  {
>  }
> +
> +static inline bool memcg_kmem_enabled(void)
> +{
> +	return false;
> +}
> +
> +static inline bool
> +__memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg, int order)
> +{
> +	return false;
> +}
> +
> +static inline void  __memcg_kmem_uncharge_page(struct page *page, int order)
> +{
> +}
> +
> +static inline void
> +__memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg, int order)
> +{
> +}

I think we shouldn't care about these for !MEMCG_KMEM. It should be
sufficient to define the main three functions bellow as return true
resp. NOOP. This would reduce the code churn a bit and also make it
better maintainable.

>  #endif /* CONFIG_MEMCG_KMEM */
> +
> +/**
> + * memcg_kmem_newpage_charge: verify if a new kmem allocation is allowed.
> + * @gfp: the gfp allocation flags.
> + * @memcg: a pointer to the memcg this was charged against.
> + * @order: allocation order.
> + *
> + * returns true if the memcg where the current task belongs can hold this
> + * allocation.
> + *
> + * We return true automatically if this allocation is not to be accounted to
> + * any memcg.
> + */
> +static __always_inline bool
> +memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg, int order)
> +{
> +	if (!memcg_kmem_enabled())
> +		return true;
> +
> +	/*
> +	 * __GFP_NOFAIL allocations will move on even if charging is not
> +	 * possible. Therefore we don't even try, and have this allocation
> +	 * unaccounted. We could in theory charge it with
> +	 * res_counter_charge_nofail, but we hope those allocations are rare,
> +	 * and won't be worth the trouble.
> +	 */
> +	if (!(gfp & __GFP_KMEMCG) || (gfp & __GFP_NOFAIL))
> +		return true;
> +	if (in_interrupt() || (!current->mm) || (current->flags & PF_KTHREAD))
> +		return true;
> +	return __memcg_kmem_newpage_charge(gfp, memcg, order);
> +}
> +
> +/**
> + * memcg_kmem_uncharge_page: uncharge pages from memcg
> + * @page: pointer to struct page being freed
> + * @order: allocation order.
> + *
> + * there is no need to specify memcg here, since it is embedded in page_cgroup
> + */
> +static __always_inline void
> +memcg_kmem_uncharge_page(struct page *page, int order)
> +{
> +	if (memcg_kmem_enabled())
> +		__memcg_kmem_uncharge_page(page, order);
> +}
> +
> +/**
> + * memcg_kmem_commit_charge: embeds correct memcg in a page
> + * @memcg: a pointer to the memcg this was charged against.
      ^^^^^^^
remove this one?

> + * @page: pointer to struct page recently allocated
> + * @memcg: the memcg structure we charged against
> + * @order: allocation order.
> + *
> + * Needs to be called after memcg_kmem_newpage_charge, regardless of success or
> + * failure of the allocation. if @page is NULL, this function will revert the
> + * charges. Otherwise, it will commit the memcg given by @memcg to the
> + * corresponding page_cgroup.
> + */
> +static __always_inline void
> +memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg, int order)
> +{
> +	if (memcg_kmem_enabled() && memcg)
> +		__memcg_kmem_commit_charge(page, memcg, order);
> +}
>  #endif /* _LINUX_MEMCONTROL_H */
>  
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f3fd354..0f36a01 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -10,6 +10,10 @@
>   * Copyright (C) 2009 Nokia Corporation
>   * Author: Kirill A. Shutemov
>   *
> + * Kernel Memory Controller
> + * Copyright (C) 2012 Parallels Inc. and Google Inc.
> + * Authors: Glauber Costa and Suleiman Souhlal
> + *
>   * This program is free software; you can redistribute it and/or modify
>   * it under the terms of the GNU General Public License as published by
>   * the Free Software Foundation; either version 2 of the License, or
> @@ -426,6 +430,9 @@ struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
>  #include <net/ip.h>
>  
>  static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
> +static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size);
> +static void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size);
> +

Why the forward declarations here? We can simply move definitions up
before they are used for the first time, can't we? Besides that they are
never used/defined from outside of KMEM_MEMCG.

>  void sock_update_memcg(struct sock *sk)
>  {
>  	if (mem_cgroup_sockets_enabled) {
> @@ -480,6 +487,110 @@ struct cg_proto *tcp_proto_cgroup(struct mem_cgroup *memcg)
>  }
>  EXPORT_SYMBOL(tcp_proto_cgroup);
>  #endif /* CONFIG_INET */
> +
> +static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
> +{
> +	return !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) &&
> +		memcg->kmem_accounted;
> +}
> +
> +/*
> + * We need to verify if the allocation against current->mm->owner's memcg is
> + * possible for the given order. But the page is not allocated yet, so we'll
> + * need a further commit step to do the final arrangements.
> + *
> + * It is possible for the task to switch cgroups in this mean time, so at
> + * commit time, we can't rely on task conversion any longer.  We'll then use
> + * the handle argument to return to the caller which cgroup we should commit
> + * against. We could also return the memcg directly and avoid the pointer
> + * passing, but a boolean return value gives better semantics considering
> + * the compiled-out case as well.
> + *
> + * Returning true means the allocation is possible.
> + */
> +bool
> +__memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
> +{
> +	struct mem_cgroup *memcg;
> +	bool ret;
> +	struct task_struct *p;

Johannes likes christmas trees ;) and /me would like to remove `p' and
use mem_cgroup_from_task(rcu_dereference(current->mm->owner)) same as we
do at other places (I guess it will be checkpatch safe).

> +
> +	*_memcg = NULL;
> +	rcu_read_lock();
> +	p = rcu_dereference(current->mm->owner);
> +	memcg = mem_cgroup_from_task(p);

mem_cgroup_from_task says it can return NULL. Do we care here? If not
then please put VM_BUG_ON(!memcg) here.

> +	rcu_read_unlock();
> +
> +	if (!memcg_can_account_kmem(memcg))
> +		return true;
> +
> +	mem_cgroup_get(memcg);

I am confused. Why do we take a reference to memcg rather than css_get
here? Ahh it is because we keep the reference while the page is
allocated, right? Comment please.

I am still not sure whether we need css_get here as well. How do you
know that the current is not moved in parallel and it is a last task in
a group which then can go away?

> +
> +	ret = memcg_charge_kmem(memcg, gfp, PAGE_SIZE << order) == 0;
> +	if (ret)
> +		*_memcg = memcg;
> +	else
> +		mem_cgroup_put(memcg);
> +
> +	return ret;
> +}
> +
> +void __memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg,
> +			      int order)
> +{
> +	struct page_cgroup *pc;
> +
> +	WARN_ON(mem_cgroup_is_root(memcg));

Why the warn? Nobody should use this directly and
memcg_kmem_commit_charge takes care of the root same as
__memcg_kmem_newpage_charge does. If it is for correctness then it
should be VM_BUG_ON.

> +
> +	/* The page allocation failed. Revert */
> +	if (!page) {
> +		memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
> +		return;
> +	}
> +
> +	pc = lookup_page_cgroup(page);
> +	lock_page_cgroup(pc);
> +	pc->mem_cgroup = memcg;
> +	SetPageCgroupUsed(pc);
> +	unlock_page_cgroup(pc);
> +}
> +
> +void __memcg_kmem_uncharge_page(struct page *page, int order)
> +{
> +	struct mem_cgroup *memcg = NULL;
> +	struct page_cgroup *pc;
> +
> +
> +	pc = lookup_page_cgroup(page);
> +	/*
> +	 * Fast unlocked return. Theoretically might have changed, have to
> +	 * check again after locking.
> +	 */
> +	if (!PageCgroupUsed(pc))
> +		return;
> +
> +	lock_page_cgroup(pc);
> +	if (PageCgroupUsed(pc)) {
> +		memcg = pc->mem_cgroup;
> +		ClearPageCgroupUsed(pc);
> +	}
> +	unlock_page_cgroup(pc);
> +
> +	/*
> +	 * Checking if kmem accounted is enabled won't work for uncharge, since
> +	 * it is possible that the user enabled kmem tracking, allocated, and
> +	 * then disabled it again.

disabling cannot happen, right?

> +	 *
> +	 * We trust if there is a memcg associated with the page, it is a valid
> +	 * allocation
> +	 */
> +	if (!memcg)
> +		return;
> +
> +	WARN_ON(mem_cgroup_is_root(memcg));

Same as above I do not see a reason for warn here. It just adds a code
and if you want it for debugging then VM_BUG_ON sounds more appropriate.
/me thinks

> +	memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
> +	mem_cgroup_put(memcg);
> +}
>  #endif /* CONFIG_MEMCG_KMEM */
>  
>  #if defined(CONFIG_INET) && defined(CONFIG_MEMCG_KMEM)
> @@ -5700,3 +5811,69 @@ static int __init enable_swap_account(char *s)
>  __setup("swapaccount=", enable_swap_account);
>  
>  #endif
> +
> +#ifdef CONFIG_MEMCG_KMEM
> +int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size)
> +{
> +	struct res_counter *fail_res;
> +	struct mem_cgroup *_memcg;
> +	int ret;
> +	bool may_oom;
> +	bool nofail = false;
> +
> +	may_oom = (gfp & __GFP_WAIT) && (gfp & __GFP_FS) &&
> +	    !(gfp & __GFP_NORETRY);

A comment please? Why __GFP_IO is not considered for example?

> +
> +	ret = 0;
> +
> +	if (!memcg)
> +		return ret;

How can we get a NULL memcg here without blowing in
__memcg_kmem_newpage_charge?

> +
> +	_memcg = memcg;
> +	ret = __mem_cgroup_try_charge(NULL, gfp, size / PAGE_SIZE,

me likes >> PAGE_SHIFT more.

> +	    &_memcg, may_oom);
> +
> +	if (ret == -EINTR)  {
> +		nofail = true;
> +		/*
> +		 * __mem_cgroup_try_charge() chosed to bypass to root due to
> +		 * OOM kill or fatal signal.  Since our only options are to
> +		 * either fail the allocation or charge it to this cgroup, do
> +		 * it as a temporary condition. But we can't fail. From a
> +		 * kmem/slab perspective, the cache has already been selected,
> +		 * by mem_cgroup_get_kmem_cache(), so it is too late to change
> +		 * our minds
> +		 */
> +		res_counter_charge_nofail(&memcg->res, size, &fail_res);
> +		if (do_swap_account)
> +			res_counter_charge_nofail(&memcg->memsw, size,
> +						  &fail_res);
> +		ret = 0;
> +	} else if (ret == -ENOMEM)
> +		return ret;
> +
> +	if (nofail)
> +		res_counter_charge_nofail(&memcg->kmem, size, &fail_res);
> +	else
> +		ret = res_counter_charge(&memcg->kmem, size, &fail_res);
> +
> +	if (ret) {
> +		res_counter_uncharge(&memcg->res, size);
> +		if (do_swap_account)
> +			res_counter_uncharge(&memcg->memsw, size);
> +	}

You could save few lines and get rid of the strange nofail by:
[...]
+		res_counter_charge_nofail(&memcg->res, size, &fail_res);
+		if (do_swap_account)
+			res_counter_charge_nofail(&memcg->memsw, size,
+						  &fail_res);
+		res_counter_charge_nofail(&memcg->kmem, size, &fail_res);
+		return 0;
+	} else if (ret == -ENOMEM)
+		return ret;
+	else
+		ret = res_counter_charge(&memcg->kmem, size, &fail_res);
+
+	if (ret) {
+		res_counter_uncharge(&memcg->res, size);
+		if (do_swap_account)
+			res_counter_uncharge(&memcg->memsw, size);
+	}

> +
> +	return ret;
> +}
> +
> +void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size)
> +{
> +	if (!memcg)
> +		return;
> +
> +	res_counter_uncharge(&memcg->kmem, size);
> +	res_counter_uncharge(&memcg->res, size);
> +	if (do_swap_account)
> +		res_counter_uncharge(&memcg->memsw, size);
> +}
> +#endif /* CONFIG_MEMCG_KMEM */
> -- 
> 1.7.11.4
> 
> --
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-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Glauber Costa]

On 09/26/2012 07:51 PM, Michal Hocko wrote:
> On Tue 18-09-12 18:04:03, Glauber Costa wrote:
>> This patch introduces infrastructure for tracking kernel memory pages to
>> a given memcg. This will happen whenever the caller includes the flag
>> __GFP_KMEMCG flag, and the task belong to a memcg other than the root.
>>
>> In memcontrol.h those functions are wrapped in inline acessors.  The
>> idea is to later on, patch those with static branches, so we don't incur
>> any overhead when no mem cgroups with limited kmem are being used.
> 
> Could you describe the API a bit here, please? I guess the
> kernel user is supposed to call memcg_kmem_newpage_charge and
> memcg_kmem_commit_charge resp. memcg_kmem_uncharge_page.
> All other kmem functions here are just helpers, right?
Yes, sir.

>>
>> [ v2: improved comments and standardized function names ]
>> [ v3: handle no longer opaque, functions not exported,
>>   even more comments ]
>> [ v4: reworked Used bit handling and surroundings for more clarity ]
>>
>> Signed-off-by: Glauber Costa <glommer@parallels.com>
>> CC: Christoph Lameter <cl@linux.com>
>> CC: Pekka Enberg <penberg@cs.helsinki.fi>
>> CC: Michal Hocko <mhocko@suse.cz>
>> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>> CC: Johannes Weiner <hannes@cmpxchg.org>
>> ---
>>  include/linux/memcontrol.h |  97 +++++++++++++++++++++++++
>>  mm/memcontrol.c            | 177 +++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 274 insertions(+)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index 8d9489f..82ede9a 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -21,6 +21,7 @@
>>  #define _LINUX_MEMCONTROL_H
>>  #include <linux/cgroup.h>
>>  #include <linux/vm_event_item.h>
>> +#include <linux/hardirq.h>
>>
>>  struct mem_cgroup;
>>  struct page_cgroup;
>> @@ -399,6 +400,17 @@ struct sock;
>>  #ifdef CONFIG_MEMCG_KMEM
>>  void sock_update_memcg(struct sock *sk);
>>  void sock_release_memcg(struct sock *sk);
>> +
>> +static inline bool memcg_kmem_enabled(void)
>> +{
>> +	return true;
>> +}
>> +
>> +extern bool __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg,
>> +					int order);
>> +extern void __memcg_kmem_commit_charge(struct page *page,
>> +				       struct mem_cgroup *memcg, int order);
>> +extern void __memcg_kmem_uncharge_page(struct page *page, int order);
>>  #else
>>  static inline void sock_update_memcg(struct sock *sk)
>>  {
>> @@ -406,6 +418,91 @@ static inline void sock_update_memcg(struct sock *sk)
>>  static inline void sock_release_memcg(struct sock *sk)
>>  {
>>  }
>> +
>> +static inline bool memcg_kmem_enabled(void)
>> +{
>> +	return false;
>> +}
>> +
>> +static inline bool
>> +__memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg, int order)
>> +{
>> +	return false;
>> +}
>> +
>> +static inline void  __memcg_kmem_uncharge_page(struct page *page, int order)
>> +{
>> +}
>> +
>> +static inline void
>> +__memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg, int order)
>> +{
>> +}
> 
> I think we shouldn't care about these for !MEMCG_KMEM. It should be
> sufficient to define the main three functions bellow as return true
> resp. NOOP. This would reduce the code churn a bit and also make it
> better maintainable.
> 

Ok.

>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index f3fd354..0f36a01 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -10,6 +10,10 @@
>>   * Copyright (C) 2009 Nokia Corporation
>>   * Author: Kirill A. Shutemov
>>   *
>> + * Kernel Memory Controller
>> + * Copyright (C) 2012 Parallels Inc. and Google Inc.
>> + * Authors: Glauber Costa and Suleiman Souhlal
>> + *
>>   * This program is free software; you can redistribute it and/or modify
>>   * it under the terms of the GNU General Public License as published by
>>   * the Free Software Foundation; either version 2 of the License, or
>> @@ -426,6 +430,9 @@ struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
>>  #include <net/ip.h>
>>  
>>  static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
>> +static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size);
>> +static void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size);
>> +
> 
> Why the forward declarations here? We can simply move definitions up
> before they are used for the first time, can't we? Besides that they are
> never used/defined from outside of KMEM_MEMCG.
>
I see your point, given the recent patch about gcc complaining about
those things. Will change.

>> +
>> +	*_memcg = NULL;
>> +	rcu_read_lock();
>> +	p = rcu_dereference(current->mm->owner);
>> +	memcg = mem_cgroup_from_task(p);
> 
> mem_cgroup_from_task says it can return NULL. Do we care here? If not
> then please put VM_BUG_ON(!memcg) here.
> 
>> +	rcu_read_unlock();
>> +
>> +	if (!memcg_can_account_kmem(memcg))
>> +		return true;
>> +
>> +	mem_cgroup_get(memcg);
> 
> I am confused. Why do we take a reference to memcg rather than css_get
> here? Ahh it is because we keep the reference while the page is
> allocated, right? Comment please.
ok.

> 
> I am still not sure whether we need css_get here as well. How do you
> know that the current is not moved in parallel and it is a last task in
> a group which then can go away?

the reference count aquired by mem_cgroup_get will still prevent the
memcg from going away, no?

>> +
>> +	/* The page allocation failed. Revert */
>> +	if (!page) {
>> +		memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
>> +		return;
>> +	}
>> +
>> +	pc = lookup_page_cgroup(page);
>> +	lock_page_cgroup(pc);
>> +	pc->mem_cgroup = memcg;
>> +	SetPageCgroupUsed(pc);
>> +	unlock_page_cgroup(pc);
>> +}
>> +
>> +void __memcg_kmem_uncharge_page(struct page *page, int order)
>> +{
>> +	struct mem_cgroup *memcg = NULL;
>> +	struct page_cgroup *pc;
>> +
>> +
>> +	pc = lookup_page_cgroup(page);
>> +	/*
>> +	 * Fast unlocked return. Theoretically might have changed, have to
>> +	 * check again after locking.
>> +	 */
>> +	if (!PageCgroupUsed(pc))
>> +		return;
>> +
>> +	lock_page_cgroup(pc);
>> +	if (PageCgroupUsed(pc)) {
>> +		memcg = pc->mem_cgroup;
>> +		ClearPageCgroupUsed(pc);
>> +	}
>> +	unlock_page_cgroup(pc);
>> +
>> +	/*
>> +	 * Checking if kmem accounted is enabled won't work for uncharge, since
>> +	 * it is possible that the user enabled kmem tracking, allocated, and
>> +	 * then disabled it again.
> 
> disabling cannot happen, right?
> 
not anymore, right. I can update the comment, but I still believe it is
a lot saner to trust information in page_cgroup.

>> +#ifdef CONFIG_MEMCG_KMEM
>> +int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size)
>> +{
>> +	struct res_counter *fail_res;
>> +	struct mem_cgroup *_memcg;
>> +	int ret;
>> +	bool may_oom;
>> +	bool nofail = false;
>> +
>> +	may_oom = (gfp & __GFP_WAIT) && (gfp & __GFP_FS) &&
>> +	    !(gfp & __GFP_NORETRY);
> 
> A comment please? Why __GFP_IO is not considered for example?
> 
> 

Actually, I believe testing for GFP_WAIT and !GFP_NORETRY would be enough.

The rationale here is, of course, under which circumstance would it be
valid to call the oom killer? Which is, if the allocation can wait, and
can retry.

> 
> You could save few lines and get rid of the strange nofail by:
> [...]
> +		res_counter_charge_nofail(&memcg->res, size, &fail_res);
> +		if (do_swap_account)
> +			res_counter_charge_nofail(&memcg->memsw, size,
> +						  &fail_res);
> +		res_counter_charge_nofail(&memcg->kmem, size, &fail_res);
> +		return 0;
> +	} else if (ret == -ENOMEM)
> +		return ret;
> +	else
> +		ret = res_counter_charge(&memcg->kmem, size, &fail_res);
> +
> +	if (ret) {
> +		res_counter_uncharge(&memcg->res, size);
> +		if (do_swap_account)
> +			res_counter_uncharge(&memcg->memsw, size);
> +	}
> 
indeed.

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Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Michal Hocko]

On Thu 27-09-12 15:31:57, Glauber Costa wrote:
> On 09/26/2012 07:51 PM, Michal Hocko wrote:
> > On Tue 18-09-12 18:04:03, Glauber Costa wrote:
[...]
> >> +	*_memcg = NULL;
> >> +	rcu_read_lock();
> >> +	p = rcu_dereference(current->mm->owner);
> >> +	memcg = mem_cgroup_from_task(p);
> > 
> > mem_cgroup_from_task says it can return NULL. Do we care here? If not
> > then please put VM_BUG_ON(!memcg) here.
> > 
> >> +	rcu_read_unlock();
> >> +
> >> +	if (!memcg_can_account_kmem(memcg))
> >> +		return true;
> >> +
> >> +	mem_cgroup_get(memcg);
> > 
> > I am confused. Why do we take a reference to memcg rather than css_get
> > here? Ahh it is because we keep the reference while the page is
> > allocated, right? Comment please.
> ok.
> 
> > 
> > I am still not sure whether we need css_get here as well. How do you
> > know that the current is not moved in parallel and it is a last task in
> > a group which then can go away?
> 
> the reference count aquired by mem_cgroup_get will still prevent the
> memcg from going away, no?

Yes but you are outside of the rcu now and we usually do css_get before
we rcu_unlock. mem_cgroup_get just makes sure the group doesn't get
deallocated but it could be gone before you call it. Or I am just
confused - these 2 levels of ref counting is really not nice.

Anyway, I have just noticed that __mem_cgroup_try_charge does
VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should
keep css ref count up as well.

> >> +	/* The page allocation failed. Revert */
> >> +	if (!page) {
> >> +		memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
> >> +		return;
> >> +	}
> >> +
> >> +	pc = lookup_page_cgroup(page);
> >> +	lock_page_cgroup(pc);
> >> +	pc->mem_cgroup = memcg;
> >> +	SetPageCgroupUsed(pc);
> >> +	unlock_page_cgroup(pc);
> >> +}
> >> +
> >> +void __memcg_kmem_uncharge_page(struct page *page, int order)
> >> +{
> >> +	struct mem_cgroup *memcg = NULL;
> >> +	struct page_cgroup *pc;
> >> +
> >> +
> >> +	pc = lookup_page_cgroup(page);
> >> +	/*
> >> +	 * Fast unlocked return. Theoretically might have changed, have to
> >> +	 * check again after locking.
> >> +	 */
> >> +	if (!PageCgroupUsed(pc))
> >> +		return;
> >> +
> >> +	lock_page_cgroup(pc);
> >> +	if (PageCgroupUsed(pc)) {
> >> +		memcg = pc->mem_cgroup;
> >> +		ClearPageCgroupUsed(pc);
> >> +	}
> >> +	unlock_page_cgroup(pc);
> >> +
> >> +	/*
> >> +	 * Checking if kmem accounted is enabled won't work for uncharge, since
> >> +	 * it is possible that the user enabled kmem tracking, allocated, and
> >> +	 * then disabled it again.
> > 
> > disabling cannot happen, right?
> > 
> not anymore, right. I can update the comment, 

yes, it is confusing

> but I still believe it is a lot saner to trust information in
> page_cgroup.

I have no objections against that. PageCgroupUsed test and using
pc->mem_cgroup is fine.

> >> +#ifdef CONFIG_MEMCG_KMEM
> >> +int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size)
> >> +{
> >> +	struct res_counter *fail_res;
> >> +	struct mem_cgroup *_memcg;
> >> +	int ret;
> >> +	bool may_oom;
> >> +	bool nofail = false;
> >> +
> >> +	may_oom = (gfp & __GFP_WAIT) && (gfp & __GFP_FS) &&
> >> +	    !(gfp & __GFP_NORETRY);
> > 
> > A comment please? Why __GFP_IO is not considered for example?
> > 
> > 
> 
> Actually, I believe testing for GFP_WAIT and !GFP_NORETRY would be enough.
> 
> The rationale here is, of course, under which circumstance would it be
> valid to call the oom killer? Which is, if the allocation can wait, and
> can retry.

Yes __GFP_WAIT is clear because memcg OOM can wait for arbitrary amount
of time (wait for userspace action on oom_control). __GFP_NORETRY
couldn't get to oom before because oom was excluded explicitely for THP
and migration didn't go through the charging path to reach the oom.
But I do agree that __GFP_NORETRY allocations shouldn't cause the OOM
because we should rather fail the allocation from kernel rather than
shoot something.

-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Glauber Costa]

On 09/27/2012 05:44 PM, Michal Hocko wrote:
>> > the reference count aquired by mem_cgroup_get will still prevent the
>> > memcg from going away, no?
> Yes but you are outside of the rcu now and we usually do css_get before
> we rcu_unlock. mem_cgroup_get just makes sure the group doesn't get
> deallocated but it could be gone before you call it. Or I am just
> confused - these 2 levels of ref counting is really not nice.
> 
> Anyway, I have just noticed that __mem_cgroup_try_charge does
> VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should
> keep css ref count up as well.
> 

IIRC, css_get will prevent the cgroup directory from being removed.
Because some allocations are expected to outlive the cgroup, we
specifically don't want that.

Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Tejun Heo]

On Fri, Sep 28, 2012 at 03:34:19PM +0400, Glauber Costa wrote:
> On 09/27/2012 05:44 PM, Michal Hocko wrote:
> > Anyway, I have just noticed that __mem_cgroup_try_charge does
> > VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should
> > keep css ref count up as well.
> 
> IIRC, css_get will prevent the cgroup directory from being removed.
> Because some allocations are expected to outlive the cgroup, we
> specifically don't want that.

That synchronous ref draining is going away.  Maybe we can do that
before kmemcg?  Michal, do you have some timeframe on mind?

Thanks.

-- 
tejun

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Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Glauber Costa]

On 09/30/2012 12:25 PM, Tejun Heo wrote:
> On Fri, Sep 28, 2012 at 03:34:19PM +0400, Glauber Costa wrote:
>> On 09/27/2012 05:44 PM, Michal Hocko wrote:
>>> Anyway, I have just noticed that __mem_cgroup_try_charge does
>>> VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should
>>> keep css ref count up as well.
>>
>> IIRC, css_get will prevent the cgroup directory from being removed.
>> Because some allocations are expected to outlive the cgroup, we
>> specifically don't want that.
> 
> That synchronous ref draining is going away.  Maybe we can do that
> before kmemcg?  Michal, do you have some timeframe on mind?
> 

Since you said yourself in other points in this thread that you are fine
with some page references outliving the cgroup in the case of slab, this
is a situation that comes with the code, not a situation that was
incidentally there, and we're making use of.


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Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Tejun Heo]

Hello, Glauber.

Sorry about late replies.  I'be been traveling for the Korean
thanksgiving holidays.

On Mon, Oct 01, 2012 at 12:28:28PM +0400, Glauber Costa wrote:
> > That synchronous ref draining is going away.  Maybe we can do that
> > before kmemcg?  Michal, do you have some timeframe on mind?
> 
> Since you said yourself in other points in this thread that you are fine
> with some page references outliving the cgroup in the case of slab, this
> is a situation that comes with the code, not a situation that was
> incidentally there, and we're making use of.

Hmmm?  Not sure what you're trying to say but I wanted to say that
this should be okay once the scheduled memcg pre_destroy change
happens and nudge Michal once more.

Thanks.

-- 
tejun

Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Michal Hocko]

On Sun 30-09-12 17:25:42, Tejun Heo wrote:
> On Fri, Sep 28, 2012 at 03:34:19PM +0400, Glauber Costa wrote:
> > On 09/27/2012 05:44 PM, Michal Hocko wrote:
> > > Anyway, I have just noticed that __mem_cgroup_try_charge does
> > > VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should
> > > keep css ref count up as well.
> > 
> > IIRC, css_get will prevent the cgroup directory from being removed.
> > Because some allocations are expected to outlive the cgroup, we
> > specifically don't want that.
> 
> That synchronous ref draining is going away.  Maybe we can do that
> before kmemcg?  Michal, do you have some timeframe on mind?

It is on my todo list but I didn't get to it yet. I am not sure we can
get rid of css_get though - will have to think about that.

> 
> Thanks.
> 
> -- 
> tejun

-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Michal Hocko]

On Fri 28-09-12 15:34:19, Glauber Costa wrote:
> On 09/27/2012 05:44 PM, Michal Hocko wrote:
> >> > the reference count aquired by mem_cgroup_get will still prevent the
> >> > memcg from going away, no?
> > Yes but you are outside of the rcu now and we usually do css_get before
> > we rcu_unlock. mem_cgroup_get just makes sure the group doesn't get
> > deallocated but it could be gone before you call it. Or I am just
> > confused - these 2 levels of ref counting is really not nice.
> > 
> > Anyway, I have just noticed that __mem_cgroup_try_charge does
> > VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should
> > keep css ref count up as well.
> > 
> 
> IIRC, css_get will prevent the cgroup directory from being removed.
> Because some allocations are expected to outlive the cgroup, we
> specifically don't want that.

Yes, but how do you guarantee that the above VM_BUG_ON doesn't trigger?
Task could have been moved to another group between mem_cgroup_from_task
and mem_cgroup_get, no?
-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Glauber Costa]

On 10/01/2012 01:48 PM, Michal Hocko wrote:
> On Fri 28-09-12 15:34:19, Glauber Costa wrote:
>> On 09/27/2012 05:44 PM, Michal Hocko wrote:
>>>>> the reference count aquired by mem_cgroup_get will still prevent the
>>>>> memcg from going away, no?
>>> Yes but you are outside of the rcu now and we usually do css_get before
>>> we rcu_unlock. mem_cgroup_get just makes sure the group doesn't get
>>> deallocated but it could be gone before you call it. Or I am just
>>> confused - these 2 levels of ref counting is really not nice.
>>>
>>> Anyway, I have just noticed that __mem_cgroup_try_charge does
>>> VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should
>>> keep css ref count up as well.
>>>
>>
>> IIRC, css_get will prevent the cgroup directory from being removed.
>> Because some allocations are expected to outlive the cgroup, we
>> specifically don't want that.
> 
> Yes, but how do you guarantee that the above VM_BUG_ON doesn't trigger?
> Task could have been moved to another group between mem_cgroup_from_task
> and mem_cgroup_get, no?
> 

Ok, after reading this again (and again), you seem to be right. It
concerns me, however, that simply getting the css would lead us to a
double get/put pair, since try_charge will have to do it anyway.

I considered just letting try_charge selecting the memcg, but that is
not really what we want, since if that memcg will fail kmem allocations,
we simply won't issue try charge, but return early.

Any immediate suggestions on how to handle this ?

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Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Michal Hocko]

On Mon 01-10-12 14:09:09, Glauber Costa wrote:
> On 10/01/2012 01:48 PM, Michal Hocko wrote:
> > On Fri 28-09-12 15:34:19, Glauber Costa wrote:
> >> On 09/27/2012 05:44 PM, Michal Hocko wrote:
> >>>>> the reference count aquired by mem_cgroup_get will still prevent the
> >>>>> memcg from going away, no?
> >>> Yes but you are outside of the rcu now and we usually do css_get before
> >>> we rcu_unlock. mem_cgroup_get just makes sure the group doesn't get
> >>> deallocated but it could be gone before you call it. Or I am just
> >>> confused - these 2 levels of ref counting is really not nice.
> >>>
> >>> Anyway, I have just noticed that __mem_cgroup_try_charge does
> >>> VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should
> >>> keep css ref count up as well.
> >>>
> >>
> >> IIRC, css_get will prevent the cgroup directory from being removed.
> >> Because some allocations are expected to outlive the cgroup, we
> >> specifically don't want that.
> > 
> > Yes, but how do you guarantee that the above VM_BUG_ON doesn't trigger?
> > Task could have been moved to another group between mem_cgroup_from_task
> > and mem_cgroup_get, no?
> > 
> 
> Ok, after reading this again (and again), you seem to be right. It
> concerns me, however, that simply getting the css would lead us to a
> double get/put pair, since try_charge will have to do it anyway.

That happens only for !*ptr case and you provide a memcg here, don't
you.

> I considered just letting try_charge selecting the memcg, but that is
> not really what we want, since if that memcg will fail kmem allocations,
> we simply won't issue try charge, but return early.
> 
> Any immediate suggestions on how to handle this ?

I would do the same thing __mem_cgroup_try_charge does.
retry:
	rcu_read_lock();
	p = rcu_dereference(mm->owner);
	if (!css_tryget(&memcg->css)) {
		rcu_read_unlock();
		goto retry;
	}
	rcu_read_unlock();

-- 
Michal Hocko
SUSE Labs

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Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Glauber Costa]

On 10/01/2012 03:51 PM, Michal Hocko wrote:
> On Mon 01-10-12 14:09:09, Glauber Costa wrote:
>> On 10/01/2012 01:48 PM, Michal Hocko wrote:
>>> On Fri 28-09-12 15:34:19, Glauber Costa wrote:
>>>> On 09/27/2012 05:44 PM, Michal Hocko wrote:
>>>>>>> the reference count aquired by mem_cgroup_get will still prevent the
>>>>>>> memcg from going away, no?
>>>>> Yes but you are outside of the rcu now and we usually do css_get before
>>>>> we rcu_unlock. mem_cgroup_get just makes sure the group doesn't get
>>>>> deallocated but it could be gone before you call it. Or I am just
>>>>> confused - these 2 levels of ref counting is really not nice.
>>>>>
>>>>> Anyway, I have just noticed that __mem_cgroup_try_charge does
>>>>> VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should
>>>>> keep css ref count up as well.
>>>>>
>>>>
>>>> IIRC, css_get will prevent the cgroup directory from being removed.
>>>> Because some allocations are expected to outlive the cgroup, we
>>>> specifically don't want that.
>>>
>>> Yes, but how do you guarantee that the above VM_BUG_ON doesn't trigger?
>>> Task could have been moved to another group between mem_cgroup_from_task
>>> and mem_cgroup_get, no?
>>>
>>
>> Ok, after reading this again (and again), you seem to be right. It
>> concerns me, however, that simply getting the css would lead us to a
>> double get/put pair, since try_charge will have to do it anyway.
> 
> That happens only for !*ptr case and you provide a memcg here, don't
> you.
> 

        if (*ptr) { /* css should be a valid one */
                memcg = *ptr;
                VM_BUG_ON(css_is_removed(&memcg->css));
                if (mem_cgroup_is_root(memcg))
                        goto done;
                if (consume_stock(memcg, nr_pages))
                        goto done;
                css_get(&memcg->css);


The way I read this, this will still issue a css_get here, unless
consume_stock suceeds (assuming non-root)

So we'd still have to have a wrapping get/put pair outside the charge.

Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Michal Hocko]

On Mon 01-10-12 15:51:20, Glauber Costa wrote:
> On 10/01/2012 03:51 PM, Michal Hocko wrote:
> > On Mon 01-10-12 14:09:09, Glauber Costa wrote:
> >> On 10/01/2012 01:48 PM, Michal Hocko wrote:
> >>> On Fri 28-09-12 15:34:19, Glauber Costa wrote:
> >>>> On 09/27/2012 05:44 PM, Michal Hocko wrote:
> >>>>>>> the reference count aquired by mem_cgroup_get will still prevent the
> >>>>>>> memcg from going away, no?
> >>>>> Yes but you are outside of the rcu now and we usually do css_get before
> >>>>> we rcu_unlock. mem_cgroup_get just makes sure the group doesn't get
> >>>>> deallocated but it could be gone before you call it. Or I am just
> >>>>> confused - these 2 levels of ref counting is really not nice.
> >>>>>
> >>>>> Anyway, I have just noticed that __mem_cgroup_try_charge does
> >>>>> VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should
> >>>>> keep css ref count up as well.
> >>>>>
> >>>>
> >>>> IIRC, css_get will prevent the cgroup directory from being removed.
> >>>> Because some allocations are expected to outlive the cgroup, we
> >>>> specifically don't want that.
> >>>
> >>> Yes, but how do you guarantee that the above VM_BUG_ON doesn't trigger?
> >>> Task could have been moved to another group between mem_cgroup_from_task
> >>> and mem_cgroup_get, no?
> >>>
> >>
> >> Ok, after reading this again (and again), you seem to be right. It
> >> concerns me, however, that simply getting the css would lead us to a
> >> double get/put pair, since try_charge will have to do it anyway.
> > 
> > That happens only for !*ptr case and you provide a memcg here, don't
> > you.
> > 
> 
>         if (*ptr) { /* css should be a valid one */
>                 memcg = *ptr;
>                 VM_BUG_ON(css_is_removed(&memcg->css));
>                 if (mem_cgroup_is_root(memcg))
>                         goto done;
>                 if (consume_stock(memcg, nr_pages))
>                         goto done;
>                 css_get(&memcg->css);
> 
> 
> The way I read this, this will still issue a css_get here, unless
> consume_stock suceeds (assuming non-root)
> 
> So we'd still have to have a wrapping get/put pair outside the charge.

That is correct but it assumes that the css is valid so somebody upwards
made sure css will not go away. This would suggest css_get is not
necessary here but I guess the primary intention here is to make the
code easier so that we do not have to check whether we took css
reference on the return path.
-- 
Michal Hocko
SUSE Labs

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Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

[Glauber Costa]

On 10/01/2012 03:58 PM, Michal Hocko wrote:
> On Mon 01-10-12 15:51:20, Glauber Costa wrote:
>> On 10/01/2012 03:51 PM, Michal Hocko wrote:
>>> On Mon 01-10-12 14:09:09, Glauber Costa wrote:
>>>> On 10/01/2012 01:48 PM, Michal Hocko wrote:
>>>>> On Fri 28-09-12 15:34:19, Glauber Costa wrote:
>>>>>> On 09/27/2012 05:44 PM, Michal Hocko wrote:
>>>>>>>>> the reference count aquired by mem_cgroup_get will still prevent the
>>>>>>>>> memcg from going away, no?
>>>>>>> Yes but you are outside of the rcu now and we usually do css_get before
>>>>>>> we rcu_unlock. mem_cgroup_get just makes sure the group doesn't get
>>>>>>> deallocated but it could be gone before you call it. Or I am just
>>>>>>> confused - these 2 levels of ref counting is really not nice.
>>>>>>>
>>>>>>> Anyway, I have just noticed that __mem_cgroup_try_charge does
>>>>>>> VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should
>>>>>>> keep css ref count up as well.
>>>>>>>
>>>>>>
>>>>>> IIRC, css_get will prevent the cgroup directory from being removed.
>>>>>> Because some allocations are expected to outlive the cgroup, we
>>>>>> specifically don't want that.
>>>>>
>>>>> Yes, but how do you guarantee that the above VM_BUG_ON doesn't trigger?
>>>>> Task could have been moved to another group between mem_cgroup_from_task
>>>>> and mem_cgroup_get, no?
>>>>>
>>>>
>>>> Ok, after reading this again (and again), you seem to be right. It
>>>> concerns me, however, that simply getting the css would lead us to a
>>>> double get/put pair, since try_charge will have to do it anyway.
>>>
>>> That happens only for !*ptr case and you provide a memcg here, don't
>>> you.
>>>
>>
>>         if (*ptr) { /* css should be a valid one */
>>                 memcg = *ptr;
>>                 VM_BUG_ON(css_is_removed(&memcg->css));
>>                 if (mem_cgroup_is_root(memcg))
>>                         goto done;
>>                 if (consume_stock(memcg, nr_pages))
>>                         goto done;
>>                 css_get(&memcg->css);
>>
>>
>> The way I read this, this will still issue a css_get here, unless
>> consume_stock suceeds (assuming non-root)
>>
>> So we'd still have to have a wrapping get/put pair outside the charge.
> 
> That is correct but it assumes that the css is valid so somebody upwards
> made sure css will not go away. This would suggest css_get is not
> necessary here but I guess the primary intention here is to make the
> code easier so that we do not have to check whether we took css
> reference on the return path.
> 
In any case, umem would also suffer from double reference, so I'm fine
taking it here as well, since a solution for that is orthogonal.

I still need mem_cgroup_get() to make sure the data structure stays
around, but we only need to do it once at first charge.

[PATCH v3 07/13] mm: Allocate kernel pages to the right memcg

[Glauber Costa]

When a process tries to allocate a page with the __GFP_KMEMCG flag, the
page allocator will call the corresponding memcg functions to validate
the allocation. Tasks in the root memcg can always proceed.

To avoid adding markers to the page - and a kmem flag that would
necessarily follow, as much as doing page_cgroup lookups for no reason,
whoever is marking its allocations with __GFP_KMEMCG flag is responsible
for telling the page allocator that this is such an allocation at
free_pages() time. This is done by the invocation of
__free_accounted_pages() and free_accounted_pages().

[ v2: inverted test order to avoid a memcg_get leak,
  free_accounted_pages simplification ]

Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
CC: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
CC: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
CC: Mel Gorman <mgorman-l3A5Bk7waGM@public.gmane.org>
Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
---
 include/linux/gfp.h |  3 +++
 mm/page_alloc.c     | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index d8eae4d..029570f 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -370,6 +370,9 @@ extern void free_pages(unsigned long addr, unsigned int order);
 extern void free_hot_cold_page(struct page *page, int cold);
 extern void free_hot_cold_page_list(struct list_head *list, int cold);
 
+extern void __free_accounted_pages(struct page *page, unsigned int order);
+extern void free_accounted_pages(unsigned long addr, unsigned int order);
+
 #define __free_page(page) __free_pages((page), 0)
 #define free_page(addr) free_pages((addr), 0)
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b0c5a52..897d8e2 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2573,6 +2573,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
 	struct page *page = NULL;
 	int migratetype = allocflags_to_migratetype(gfp_mask);
 	unsigned int cpuset_mems_cookie;
+	struct mem_cgroup *memcg = NULL;
 
 	gfp_mask &= gfp_allowed_mask;
 
@@ -2591,6 +2592,13 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
 	if (unlikely(!zonelist->_zonerefs->zone))
 		return NULL;
 
+	/*
+	 * Will only have any effect when __GFP_KMEMCG is set.  This is
+	 * verified in the (always inline) callee
+	 */
+	if (!memcg_kmem_newpage_charge(gfp_mask, &memcg, order))
+		return NULL;
+
 retry_cpuset:
 	cpuset_mems_cookie = get_mems_allowed();
 
@@ -2624,6 +2632,8 @@ out:
 	if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
 		goto retry_cpuset;
 
+	memcg_kmem_commit_charge(page, memcg, order);
+
 	return page;
 }
 EXPORT_SYMBOL(__alloc_pages_nodemask);
@@ -2676,6 +2686,31 @@ void free_pages(unsigned long addr, unsigned int order)
 
 EXPORT_SYMBOL(free_pages);
 
+/*
+ * __free_accounted_pages and free_accounted_pages will free pages allocated
+ * with __GFP_KMEMCG.
+ *
+ * Those pages are accounted to a particular memcg, embedded in the
+ * corresponding page_cgroup. To avoid adding a hit in the allocator to search
+ * for that information only to find out that it is NULL for users who have no
+ * interest in that whatsoever, we provide these functions.
+ *
+ * The caller knows better which flags it relies on.
+ */
+void __free_accounted_pages(struct page *page, unsigned int order)
+{
+	memcg_kmem_uncharge_page(page, order);
+	__free_pages(page, order);
+}
+
+void free_accounted_pages(unsigned long addr, unsigned int order)
+{
+	if (addr != 0) {
+		VM_BUG_ON(!virt_addr_valid((void *)addr));
+		__free_accounted_pages(virt_to_page((void *)addr), order);
+	}
+}
+
 static void *make_alloc_exact(unsigned long addr, unsigned order, size_t size)
 {
 	if (addr) {
-- 
1.7.11.4

Re: [PATCH v3 07/13] mm: Allocate kernel pages to the right memcg

[Mel Gorman]

On Tue, Sep 18, 2012 at 06:04:04PM +0400, Glauber Costa wrote:
> When a process tries to allocate a page with the __GFP_KMEMCG flag, the
> page allocator will call the corresponding memcg functions to validate
> the allocation. Tasks in the root memcg can always proceed.
> 
> To avoid adding markers to the page - and a kmem flag that would
> necessarily follow, as much as doing page_cgroup lookups for no reason,
> whoever is marking its allocations with __GFP_KMEMCG flag is responsible
> for telling the page allocator that this is such an allocation at
> free_pages() time. This is done by the invocation of
> __free_accounted_pages() and free_accounted_pages().
> 
> [ v2: inverted test order to avoid a memcg_get leak,
>   free_accounted_pages simplification ]
> 
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> CC: Christoph Lameter <cl@linux.com>
> CC: Pekka Enberg <penberg@cs.helsinki.fi>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Suleiman Souhlal <suleiman@google.com>
> CC: Mel Gorman <mgorman@suse.de>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
>  include/linux/gfp.h |  3 +++
>  mm/page_alloc.c     | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index d8eae4d..029570f 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -370,6 +370,9 @@ extern void free_pages(unsigned long addr, unsigned int order);
>  extern void free_hot_cold_page(struct page *page, int cold);
>  extern void free_hot_cold_page_list(struct list_head *list, int cold);
>  
> +extern void __free_accounted_pages(struct page *page, unsigned int order);
> +extern void free_accounted_pages(unsigned long addr, unsigned int order);
> +
>  #define __free_page(page) __free_pages((page), 0)
>  #define free_page(addr) free_pages((addr), 0)
>  
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b0c5a52..897d8e2 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2573,6 +2573,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>  	struct page *page = NULL;
>  	int migratetype = allocflags_to_migratetype(gfp_mask);
>  	unsigned int cpuset_mems_cookie;
> +	struct mem_cgroup *memcg = NULL;
>  
>  	gfp_mask &= gfp_allowed_mask;
>  
> @@ -2591,6 +2592,13 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>  	if (unlikely(!zonelist->_zonerefs->zone))
>  		return NULL;
>  
> +	/*
> +	 * Will only have any effect when __GFP_KMEMCG is set.  This is
> +	 * verified in the (always inline) callee
> +	 */
> +	if (!memcg_kmem_newpage_charge(gfp_mask, &memcg, order))
> +		return NULL;
> +

1. returns quickly if memcg disabled
2. returns quickly if !__GFP_KMEMCG
3. returns quickly for kernel threads and interrupts

I'm expecting that these paths are completely dead when kmem accounting
is off so

Acked-by: Mel Gorman <mgorman@suse.de>


That said, it's not directly related to this patch but I would suggest that
you also check for TIF_MEMDIE in memcg_kmem_newpage_charge. It would be very
silly if a process failed to exit because it couldn't allocate a page it
needed. I expect that such a case is impossible today but it might change in
the future. If you're doing another revision, an extra check would not hurt.

It's difficult to predict if it should be making all the checks that
gfp_to_alloc_flags() does but you might need to in the future so keep it
in mind.




>  retry_cpuset:
>  	cpuset_mems_cookie = get_mems_allowed();
>  
> @@ -2624,6 +2632,8 @@ out:
>  	if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
>  		goto retry_cpuset;
>  
> +	memcg_kmem_commit_charge(page, memcg, order);
> +
>  	return page;

Ok.

>  }
>  EXPORT_SYMBOL(__alloc_pages_nodemask);
> @@ -2676,6 +2686,31 @@ void free_pages(unsigned long addr, unsigned int order)
>  
>  EXPORT_SYMBOL(free_pages);
>  
> +/*
> + * __free_accounted_pages and free_accounted_pages will free pages allocated
> + * with __GFP_KMEMCG.
> + *
> + * Those pages are accounted to a particular memcg, embedded in the
> + * corresponding page_cgroup. To avoid adding a hit in the allocator to search
> + * for that information only to find out that it is NULL for users who have no
> + * interest in that whatsoever, we provide these functions.
> + *
> + * The caller knows better which flags it relies on.
> + */
> +void __free_accounted_pages(struct page *page, unsigned int order)
> +{
> +	memcg_kmem_uncharge_page(page, order);
> +	__free_pages(page, order);
> +}
> +
> +void free_accounted_pages(unsigned long addr, unsigned int order)
> +{
> +	if (addr != 0) {
> +		VM_BUG_ON(!virt_addr_valid((void *)addr));

This is probably overkill. If it's invalid, the next line is likely to
blow up anyway. It's no biggie.

> +		__free_accounted_pages(virt_to_page((void *)addr), order);
> +	}
> +}
> +
>  static void *make_alloc_exact(unsigned long addr, unsigned order, size_t size)
>  {
>  	if (addr) {
> -- 
> 1.7.11.4
> 

-- 
Mel Gorman
SUSE Labs

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Re: [PATCH v3 07/13] mm: Allocate kernel pages to the right memcg

[Glauber Costa]

On 09/27/2012 05:50 PM, Mel Gorman wrote:
>> +void __free_accounted_pages(struct page *page, unsigned int order)
>> > +{
>> > +	memcg_kmem_uncharge_page(page, order);
>> > +	__free_pages(page, order);
>> > +}
>> > +
>> > +void free_accounted_pages(unsigned long addr, unsigned int order)
>> > +{
>> > +	if (addr != 0) {
>> > +		VM_BUG_ON(!virt_addr_valid((void *)addr));
> This is probably overkill. If it's invalid, the next line is likely to
> blow up anyway. It's no biggie.
> 

So this is here because it is in free_pages() as well. If it blows, at
least we know precisely why (if debugging), and VM_BUG_ON() is only
compiled in when CONFIG_DEBUG_VM.

But I'm fine with either.
Should it stay or should it go ?

Re: [PATCH v3 07/13] mm: Allocate kernel pages to the right memcg

[Mel Gorman]

On Fri, Sep 28, 2012 at 01:43:47PM +0400, Glauber Costa wrote:
> On 09/27/2012 05:50 PM, Mel Gorman wrote:
> >> +void __free_accounted_pages(struct page *page, unsigned int order)
> >> > +{
> >> > +	memcg_kmem_uncharge_page(page, order);
> >> > +	__free_pages(page, order);
> >> > +}
> >> > +
> >> > +void free_accounted_pages(unsigned long addr, unsigned int order)
> >> > +{
> >> > +	if (addr != 0) {
> >> > +		VM_BUG_ON(!virt_addr_valid((void *)addr));
> > This is probably overkill. If it's invalid, the next line is likely to
> > blow up anyway. It's no biggie.
> > 
> 
> So this is here because it is in free_pages() as well. If it blows, at
> least we know precisely why (if debugging), and VM_BUG_ON() is only
> compiled in when CONFIG_DEBUG_VM.
> 

Ah, I see.

> But I'm fine with either.
> Should it stay or should it go ?
> 

It can stay. It makes sense that it look similar to free_pages() and as
you say, it makes debugging marginally easier.


-- 
Mel Gorman
SUSE Labs

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Re: [PATCH v3 07/13] mm: Allocate kernel pages to the right memcg

[Michal Hocko]

On Tue 18-09-12 18:04:04, Glauber Costa wrote:
> When a process tries to allocate a page with the __GFP_KMEMCG flag, the
> page allocator will call the corresponding memcg functions to validate
> the allocation. Tasks in the root memcg can always proceed.
> 
> To avoid adding markers to the page - and a kmem flag that would
> necessarily follow, as much as doing page_cgroup lookups for no reason,
> whoever is marking its allocations with __GFP_KMEMCG flag is responsible
> for telling the page allocator that this is such an allocation at
> free_pages() time. This is done by the invocation of
> __free_accounted_pages() and free_accounted_pages().
> 
> [ v2: inverted test order to avoid a memcg_get leak,
>   free_accounted_pages simplification ]
> 
> Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
> CC: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
> CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
> CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
> CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> CC: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> CC: Mel Gorman <mgorman-l3A5Bk7waGM@public.gmane.org>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>

Acked-by: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>

Thanks!

> ---
>  include/linux/gfp.h |  3 +++
>  mm/page_alloc.c     | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index d8eae4d..029570f 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -370,6 +370,9 @@ extern void free_pages(unsigned long addr, unsigned int order);
>  extern void free_hot_cold_page(struct page *page, int cold);
>  extern void free_hot_cold_page_list(struct list_head *list, int cold);
>  
> +extern void __free_accounted_pages(struct page *page, unsigned int order);
> +extern void free_accounted_pages(unsigned long addr, unsigned int order);
> +
>  #define __free_page(page) __free_pages((page), 0)
>  #define free_page(addr) free_pages((addr), 0)
>  
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b0c5a52..897d8e2 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2573,6 +2573,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>  	struct page *page = NULL;
>  	int migratetype = allocflags_to_migratetype(gfp_mask);
>  	unsigned int cpuset_mems_cookie;
> +	struct mem_cgroup *memcg = NULL;
>  
>  	gfp_mask &= gfp_allowed_mask;
>  
> @@ -2591,6 +2592,13 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>  	if (unlikely(!zonelist->_zonerefs->zone))
>  		return NULL;
>  
> +	/*
> +	 * Will only have any effect when __GFP_KMEMCG is set.  This is
> +	 * verified in the (always inline) callee
> +	 */
> +	if (!memcg_kmem_newpage_charge(gfp_mask, &memcg, order))
> +		return NULL;
> +
>  retry_cpuset:
>  	cpuset_mems_cookie = get_mems_allowed();
>  
> @@ -2624,6 +2632,8 @@ out:
>  	if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
>  		goto retry_cpuset;
>  
> +	memcg_kmem_commit_charge(page, memcg, order);
> +
>  	return page;
>  }
>  EXPORT_SYMBOL(__alloc_pages_nodemask);
> @@ -2676,6 +2686,31 @@ void free_pages(unsigned long addr, unsigned int order)
>  
>  EXPORT_SYMBOL(free_pages);
>  
> +/*
> + * __free_accounted_pages and free_accounted_pages will free pages allocated
> + * with __GFP_KMEMCG.
> + *
> + * Those pages are accounted to a particular memcg, embedded in the
> + * corresponding page_cgroup. To avoid adding a hit in the allocator to search
> + * for that information only to find out that it is NULL for users who have no
> + * interest in that whatsoever, we provide these functions.
> + *
> + * The caller knows better which flags it relies on.
> + */
> +void __free_accounted_pages(struct page *page, unsigned int order)
> +{
> +	memcg_kmem_uncharge_page(page, order);
> +	__free_pages(page, order);
> +}
> +
> +void free_accounted_pages(unsigned long addr, unsigned int order)
> +{
> +	if (addr != 0) {
> +		VM_BUG_ON(!virt_addr_valid((void *)addr));
> +		__free_accounted_pages(virt_to_page((void *)addr), order);
> +	}
> +}
> +
>  static void *make_alloc_exact(unsigned long addr, unsigned order, size_t size)
>  {
>  	if (addr) {
> -- 
> 1.7.11.4
> 
> --
> To unsubscribe from this list: send the line "unsubscribe cgroups" in
> the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Michal Hocko
SUSE Labs

[PATCH v3 08/13] res_counter: return amount of charges after res_counter_uncharge

[Glauber Costa]

It is useful to know how many charges are still left after a call to
res_counter_uncharge. While it is possible to issue a res_counter_read
after uncharge, this is racy. It would be better if uncharge itself
would tell us what the current status is.

Since the current return value is void, we don't need to worry about
anything breaking due to this change: nobody relied on that, and only
users appearing from now on will be checking this value.

Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
CC: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
---
 Documentation/cgroups/resource_counter.txt |  7 ++++---
 include/linux/res_counter.h                | 12 +++++++-----
 kernel/res_counter.c                       | 20 +++++++++++++-------
 3 files changed, 24 insertions(+), 15 deletions(-)

diff --git a/Documentation/cgroups/resource_counter.txt b/Documentation/cgroups/resource_counter.txt
index 0c4a344..c4d99ed 100644
--- a/Documentation/cgroups/resource_counter.txt
+++ b/Documentation/cgroups/resource_counter.txt
@@ -83,16 +83,17 @@ to work with it.
 	res_counter->lock internally (it must be called with res_counter->lock
 	held). The force parameter indicates whether we can bypass the limit.
 
- e. void res_counter_uncharge[_locked]
+ e. u64 res_counter_uncharge[_locked]
 			(struct res_counter *rc, unsigned long val)
 
 	When a resource is released (freed) it should be de-accounted
 	from the resource counter it was accounted to.  This is called
-	"uncharging".
+	"uncharging". The return value of this function indicate the amount
+	of charges still present in the counter.
 
 	The _locked routines imply that the res_counter->lock is taken.
 
- f. void res_counter_uncharge_until
+ f. u64 res_counter_uncharge_until
 		(struct res_counter *rc, struct res_counter *top,
 		 unsinged long val)
 
diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
index 7d7fbe2..4b173b6 100644
--- a/include/linux/res_counter.h
+++ b/include/linux/res_counter.h
@@ -130,14 +130,16 @@ int res_counter_charge_nofail(struct res_counter *counter,
  *
  * these calls check for usage underflow and show a warning on the console
  * _locked call expects the counter->lock to be taken
+ *
+ * returns the total charges still present in @counter.
  */
 
-void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val);
-void res_counter_uncharge(struct res_counter *counter, unsigned long val);
+u64 res_counter_uncharge_locked(struct res_counter *counter, unsigned long val);
+u64 res_counter_uncharge(struct res_counter *counter, unsigned long val);
 
-void res_counter_uncharge_until(struct res_counter *counter,
-				struct res_counter *top,
-				unsigned long val);
+u64 res_counter_uncharge_until(struct res_counter *counter,
+			       struct res_counter *top,
+			       unsigned long val);
 /**
  * res_counter_margin - calculate chargeable space of a counter
  * @cnt: the counter
diff --git a/kernel/res_counter.c b/kernel/res_counter.c
index ad581aa..7b3d6dc 100644
--- a/kernel/res_counter.c
+++ b/kernel/res_counter.c
@@ -86,33 +86,39 @@ int res_counter_charge_nofail(struct res_counter *counter, unsigned long val,
 	return __res_counter_charge(counter, val, limit_fail_at, true);
 }
 
-void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val)
+u64 res_counter_uncharge_locked(struct res_counter *counter, unsigned long val)
 {
 	if (WARN_ON(counter->usage < val))
 		val = counter->usage;
 
 	counter->usage -= val;
+	return counter->usage;
 }
 
-void res_counter_uncharge_until(struct res_counter *counter,
-				struct res_counter *top,
-				unsigned long val)
+u64 res_counter_uncharge_until(struct res_counter *counter,
+			       struct res_counter *top,
+			       unsigned long val)
 {
 	unsigned long flags;
 	struct res_counter *c;
+	u64 ret = 0;
 
 	local_irq_save(flags);
 	for (c = counter; c != top; c = c->parent) {
+		u64 r;
 		spin_lock(&c->lock);
-		res_counter_uncharge_locked(c, val);
+		r = res_counter_uncharge_locked(c, val);
+		if (c == counter)
+			ret = r;
 		spin_unlock(&c->lock);
 	}
 	local_irq_restore(flags);
+	return ret;
 }
 
-void res_counter_uncharge(struct res_counter *counter, unsigned long val)
+u64 res_counter_uncharge(struct res_counter *counter, unsigned long val)
 {
-	res_counter_uncharge_until(counter, NULL, val);
+	return res_counter_uncharge_until(counter, NULL, val);
 }
 
 static inline unsigned long long *
-- 
1.7.11.4

Re: [PATCH v3 08/13] res_counter: return amount of charges after res_counter_uncharge

[Michal Hocko]

On Tue 18-09-12 18:04:05, Glauber Costa wrote:
> It is useful to know how many charges are still left after a call to
> res_counter_uncharge. 

> While it is possible to issue a res_counter_read
> after uncharge, this is racy. It would be better if uncharge itself
> would tell us what the current status is.

Well I am not sure how less racy it would be if you return the old
value. It could be out of date when you read it, right? (this is even
more visible with res_counter_uncharge_until)
res_counter_read_u64 uses locks only for 32b when your change could help
to reduce lock contention. Other than that it is just res_counter_member
which is one cmp and a dereference. Sure you safe something but it is
barely noticable I guess.

I am not saying I do not like this change I just think that the
above part of the changelog doesn't fit. So it would be much better if
you tell us why this is needed for your patchset because the usage is
not part of the patch.

> Since the current return value is void, we don't need to worry about
> anything breaking due to this change: nobody relied on that, and only
> users appearing from now on will be checking this value.
> 
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Suleiman Souhlal <suleiman@google.com>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
>  Documentation/cgroups/resource_counter.txt |  7 ++++---
>  include/linux/res_counter.h                | 12 +++++++-----
>  kernel/res_counter.c                       | 20 +++++++++++++-------
>  3 files changed, 24 insertions(+), 15 deletions(-)
> 
> diff --git a/Documentation/cgroups/resource_counter.txt b/Documentation/cgroups/resource_counter.txt
> index 0c4a344..c4d99ed 100644
> --- a/Documentation/cgroups/resource_counter.txt
> +++ b/Documentation/cgroups/resource_counter.txt
> @@ -83,16 +83,17 @@ to work with it.
>  	res_counter->lock internally (it must be called with res_counter->lock
>  	held). The force parameter indicates whether we can bypass the limit.
>  
> - e. void res_counter_uncharge[_locked]
> + e. u64 res_counter_uncharge[_locked]
>  			(struct res_counter *rc, unsigned long val)
>  
>  	When a resource is released (freed) it should be de-accounted
>  	from the resource counter it was accounted to.  This is called
> -	"uncharging".
> +	"uncharging". The return value of this function indicate the amount
> +	of charges still present in the counter.
>  
>  	The _locked routines imply that the res_counter->lock is taken.
>  
> - f. void res_counter_uncharge_until
> + f. u64 res_counter_uncharge_until
>  		(struct res_counter *rc, struct res_counter *top,
>  		 unsinged long val)
>  
> diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
> index 7d7fbe2..4b173b6 100644
> --- a/include/linux/res_counter.h
> +++ b/include/linux/res_counter.h
> @@ -130,14 +130,16 @@ int res_counter_charge_nofail(struct res_counter *counter,
>   *
>   * these calls check for usage underflow and show a warning on the console
>   * _locked call expects the counter->lock to be taken
> + *
> + * returns the total charges still present in @counter.
>   */
>  
> -void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val);
> -void res_counter_uncharge(struct res_counter *counter, unsigned long val);
> +u64 res_counter_uncharge_locked(struct res_counter *counter, unsigned long val);
> +u64 res_counter_uncharge(struct res_counter *counter, unsigned long val);
>  
> -void res_counter_uncharge_until(struct res_counter *counter,
> -				struct res_counter *top,
> -				unsigned long val);
> +u64 res_counter_uncharge_until(struct res_counter *counter,
> +			       struct res_counter *top,
> +			       unsigned long val);
>  /**
>   * res_counter_margin - calculate chargeable space of a counter
>   * @cnt: the counter
> diff --git a/kernel/res_counter.c b/kernel/res_counter.c
> index ad581aa..7b3d6dc 100644
> --- a/kernel/res_counter.c
> +++ b/kernel/res_counter.c
> @@ -86,33 +86,39 @@ int res_counter_charge_nofail(struct res_counter *counter, unsigned long val,
>  	return __res_counter_charge(counter, val, limit_fail_at, true);
>  }
>  
> -void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val)
> +u64 res_counter_uncharge_locked(struct res_counter *counter, unsigned long val)
>  {
>  	if (WARN_ON(counter->usage < val))
>  		val = counter->usage;
>  
>  	counter->usage -= val;
> +	return counter->usage;
>  }
>  
> -void res_counter_uncharge_until(struct res_counter *counter,
> -				struct res_counter *top,
> -				unsigned long val)
> +u64 res_counter_uncharge_until(struct res_counter *counter,
> +			       struct res_counter *top,
> +			       unsigned long val)
>  {
>  	unsigned long flags;
>  	struct res_counter *c;
> +	u64 ret = 0;
>  
>  	local_irq_save(flags);
>  	for (c = counter; c != top; c = c->parent) {
> +		u64 r;
>  		spin_lock(&c->lock);
> -		res_counter_uncharge_locked(c, val);
> +		r = res_counter_uncharge_locked(c, val);
> +		if (c == counter)
> +			ret = r;
>  		spin_unlock(&c->lock);
>  	}
>  	local_irq_restore(flags);
> +	return ret;
>  }
>  
> -void res_counter_uncharge(struct res_counter *counter, unsigned long val)
> +u64 res_counter_uncharge(struct res_counter *counter, unsigned long val)
>  {
> -	res_counter_uncharge_until(counter, NULL, val);
> +	return res_counter_uncharge_until(counter, NULL, val);
>  }
>  
>  static inline unsigned long long *
> -- 
> 1.7.11.4
> 
> --
> To unsubscribe from this list: send the line "unsubscribe cgroups" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Michal Hocko
SUSE Labs

--
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Re: [PATCH v3 08/13] res_counter: return amount of charges after res_counter_uncharge

[Glauber Costa]

On 10/01/2012 02:00 PM, Michal Hocko wrote:
> On Tue 18-09-12 18:04:05, Glauber Costa wrote:
>> It is useful to know how many charges are still left after a call to
>> res_counter_uncharge. 
> 
>> While it is possible to issue a res_counter_read
>> after uncharge, this is racy. It would be better if uncharge itself
>> would tell us what the current status is.
> 
> Well I am not sure how less racy it would be if you return the old
> value. It could be out of date when you read it, right? (this is even
> more visible with res_counter_uncharge_until)
> res_counter_read_u64 uses locks only for 32b when your change could help
> to reduce lock contention. Other than that it is just res_counter_member
> which is one cmp and a dereference. Sure you safe something but it is
> barely noticable I guess.
> 

Sure it can. But this is the same semantics of the atomic updates, which
were always considered to be good enough for cases like this.


> I am not saying I do not like this change I just think that the
> above part of the changelog doesn't fit. So it would be much better if
> you tell us why this is needed for your patchset because the usage is
> not part of the patch.
> 

I can update the changelog, for sure. But for the record, this has the
goal of taking the get/put pair out of the charge/uncharge path.

If I have 8k of data, and two threads decrement 4k each, a update + read
may return 0 for both. With this patch, only one of them will see 0, and
will proceed with the reference drop.

Again, this is the same semantics as all of the atomic variables in the
kernel.


>> Since the current return value is void, we don't need to worry about
>> anything breaking due to this change: nobody relied on that, and only
>> users appearing from now on will be checking this value.
>>
>> Signed-off-by: Glauber Costa <glommer@parallels.com>
>> CC: Michal Hocko <mhocko@suse.cz>
>> CC: Johannes Weiner <hannes@cmpxchg.org>
>> CC: Suleiman Souhlal <suleiman@google.com>
>> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>> ---
>>  Documentation/cgroups/resource_counter.txt |  7 ++++---
>>  include/linux/res_counter.h                | 12 +++++++-----
>>  kernel/res_counter.c                       | 20 +++++++++++++-------
>>  3 files changed, 24 insertions(+), 15 deletions(-)
>>
>> diff --git a/Documentation/cgroups/resource_counter.txt b/Documentation/cgroups/resource_counter.txt
>> index 0c4a344..c4d99ed 100644
>> --- a/Documentation/cgroups/resource_counter.txt
>> +++ b/Documentation/cgroups/resource_counter.txt
>> @@ -83,16 +83,17 @@ to work with it.
>>  	res_counter->lock internally (it must be called with res_counter->lock
>>  	held). The force parameter indicates whether we can bypass the limit.
>>  
>> - e. void res_counter_uncharge[_locked]
>> + e. u64 res_counter_uncharge[_locked]
>>  			(struct res_counter *rc, unsigned long val)
>>  
>>  	When a resource is released (freed) it should be de-accounted
>>  	from the resource counter it was accounted to.  This is called
>> -	"uncharging".
>> +	"uncharging". The return value of this function indicate the amount
>> +	of charges still present in the counter.
>>  
>>  	The _locked routines imply that the res_counter->lock is taken.
>>  
>> - f. void res_counter_uncharge_until
>> + f. u64 res_counter_uncharge_until
>>  		(struct res_counter *rc, struct res_counter *top,
>>  		 unsinged long val)
>>  
>> diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
>> index 7d7fbe2..4b173b6 100644
>> --- a/include/linux/res_counter.h
>> +++ b/include/linux/res_counter.h
>> @@ -130,14 +130,16 @@ int res_counter_charge_nofail(struct res_counter *counter,
>>   *
>>   * these calls check for usage underflow and show a warning on the console
>>   * _locked call expects the counter->lock to be taken
>> + *
>> + * returns the total charges still present in @counter.
>>   */
>>  
>> -void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val);
>> -void res_counter_uncharge(struct res_counter *counter, unsigned long val);
>> +u64 res_counter_uncharge_locked(struct res_counter *counter, unsigned long val);
>> +u64 res_counter_uncharge(struct res_counter *counter, unsigned long val);
>>  
>> -void res_counter_uncharge_until(struct res_counter *counter,
>> -				struct res_counter *top,
>> -				unsigned long val);
>> +u64 res_counter_uncharge_until(struct res_counter *counter,
>> +			       struct res_counter *top,
>> +			       unsigned long val);
>>  /**
>>   * res_counter_margin - calculate chargeable space of a counter
>>   * @cnt: the counter
>> diff --git a/kernel/res_counter.c b/kernel/res_counter.c
>> index ad581aa..7b3d6dc 100644
>> --- a/kernel/res_counter.c
>> +++ b/kernel/res_counter.c
>> @@ -86,33 +86,39 @@ int res_counter_charge_nofail(struct res_counter *counter, unsigned long val,
>>  	return __res_counter_charge(counter, val, limit_fail_at, true);
>>  }
>>  
>> -void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val)
>> +u64 res_counter_uncharge_locked(struct res_counter *counter, unsigned long val)
>>  {
>>  	if (WARN_ON(counter->usage < val))
>>  		val = counter->usage;
>>  
>>  	counter->usage -= val;
>> +	return counter->usage;
>>  }
>>  
>> -void res_counter_uncharge_until(struct res_counter *counter,
>> -				struct res_counter *top,
>> -				unsigned long val)
>> +u64 res_counter_uncharge_until(struct res_counter *counter,
>> +			       struct res_counter *top,
>> +			       unsigned long val)
>>  {
>>  	unsigned long flags;
>>  	struct res_counter *c;
>> +	u64 ret = 0;
>>  
>>  	local_irq_save(flags);
>>  	for (c = counter; c != top; c = c->parent) {
>> +		u64 r;
>>  		spin_lock(&c->lock);
>> -		res_counter_uncharge_locked(c, val);
>> +		r = res_counter_uncharge_locked(c, val);
>> +		if (c == counter)
>> +			ret = r;
>>  		spin_unlock(&c->lock);
>>  	}
>>  	local_irq_restore(flags);
>> +	return ret;
>>  }
>>  
>> -void res_counter_uncharge(struct res_counter *counter, unsigned long val)
>> +u64 res_counter_uncharge(struct res_counter *counter, unsigned long val)
>>  {
>> -	res_counter_uncharge_until(counter, NULL, val);
>> +	return res_counter_uncharge_until(counter, NULL, val);
>>  }
>>  
>>  static inline unsigned long long *
>> -- 
>> 1.7.11.4
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe cgroups" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

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[PATCH v3 09/13] memcg: kmem accounting lifecycle management

[Glauber Costa]

Because the assignment: memcg->kmem_accounted = true is done after the
jump labels increment, we guarantee that the root memcg will always be
selected until all call sites are patched (see memcg_kmem_enabled).
This guarantees that no mischarges are applied.

Jump label decrement happens when the last reference count from the
memcg dies. This will only happen when the caches are all dead.

-> /cgroups/memory/A/B/C

* kmem limit set at A,
* A and B have no tasks,
* span a new task in in C.

Because kmem_accounted is a boolean that was not set for C, no
accounting would be done. This is, however, not what we expect.

The basic idea, is that when a cgroup is limited, we walk the tree
downwards and make sure that we store the information about the parent
being limited in kmem_accounted.

We do the reverse operation when a formerly limited cgroup becomes
unlimited.

Since kmem charges may outlive the cgroup existance, we need to be extra
careful to guarantee the memcg object will stay around for as long as
needed. Up to now, we were using a mem_cgroup_get()/put() pair in charge
and uncharge operations.

Although this guarantees that the object will be around until the last
call to unchage, this means an atomic update in every charge. We can do
better than that if we only issue get() in the first charge, and then
put() when the last charge finally goes away.

[ v3: merged all lifecycle related patches in one ]

Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
CC: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
CC: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
---
 mm/memcontrol.c | 123 +++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 112 insertions(+), 11 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0f36a01..720e4bb 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -287,7 +287,8 @@ struct mem_cgroup {
 	 * Should the accounting and control be hierarchical, per subtree?
 	 */
 	bool use_hierarchy;
-	bool kmem_accounted;
+
+	unsigned long kmem_accounted; /* See KMEM_ACCOUNTED_*, below */
 
 	bool		oom_lock;
 	atomic_t	under_oom;
@@ -340,6 +341,43 @@ struct mem_cgroup {
 #endif
 };
 
+enum {
+	KMEM_ACCOUNTED_ACTIVE = 0, /* accounted by this cgroup itself */
+	KMEM_ACCOUNTED_PARENT, /* one of its parents is active */
+	KMEM_ACCOUNTED_DEAD, /* dead memcg, pending kmem charges */
+};
+
+/* bits 0 and 1 */
+#define KMEM_ACCOUNTED_MASK 0x3
+
+#ifdef CONFIG_MEMCG_KMEM
+static bool memcg_kmem_set_active(struct mem_cgroup *memcg)
+{
+	return !test_and_set_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_accounted);
+}
+
+static bool memcg_kmem_is_accounted(struct mem_cgroup *memcg)
+{
+	return test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_accounted);
+}
+
+static void memcg_kmem_set_active_parent(struct mem_cgroup *memcg)
+{
+	set_bit(KMEM_ACCOUNTED_PARENT, &memcg->kmem_accounted);
+}
+
+static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
+{
+	if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_accounted))
+		set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_accounted);
+}
+
+static bool memcg_kmem_dead(struct mem_cgroup *memcg)
+{
+	return test_and_clear_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_accounted);
+}
+#endif /* CONFIG_MEMCG_KMEM */
+
 /* Stuffs for move charges at task migration. */
 /*
  * Types of charges to be moved. "move_charge_at_immitgrate" is treated as a
@@ -491,7 +529,7 @@ EXPORT_SYMBOL(tcp_proto_cgroup);
 static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
 {
 	return !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) &&
-		memcg->kmem_accounted;
+		 (memcg->kmem_accounted & (KMEM_ACCOUNTED_MASK));
 }
 
 /*
@@ -524,13 +562,9 @@ __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
 	if (!memcg_can_account_kmem(memcg))
 		return true;
 
-	mem_cgroup_get(memcg);
-
 	ret = memcg_charge_kmem(memcg, gfp, PAGE_SIZE << order) == 0;
 	if (ret)
 		*_memcg = memcg;
-	else
-		mem_cgroup_put(memcg);
 
 	return ret;
 }
@@ -589,7 +623,6 @@ void __memcg_kmem_uncharge_page(struct page *page, int order)
 
 	WARN_ON(mem_cgroup_is_root(memcg));
 	memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
-	mem_cgroup_put(memcg);
 }
 #endif /* CONFIG_MEMCG_KMEM */
 
@@ -4077,6 +4110,40 @@ static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
 	len = scnprintf(str, sizeof(str), "%llu\n", (unsigned long long)val);
 	return simple_read_from_buffer(buf, nbytes, ppos, str, len);
 }
+
+static void memcg_update_kmem_limit(struct mem_cgroup *memcg, u64 val)
+{
+#ifdef CONFIG_MEMCG_KMEM
+	struct mem_cgroup *iter;
+
+	/*
+	 * When we are doing hierarchical accounting, with an hierarchy like
+	 * A/B/C, we need to start accounting kernel memory all the way up to C
+	 * in case A start being accounted.
+	 *
+	 * So when we the cgroup first gets to be unlimited, we walk all the
+	 * children of the current memcg and enable kmem accounting for them.
+	 * Note that a separate bit is used there to indicate that the
+	 * accounting happens due to the parent being accounted.
+	 *
+	 * note that memcg_kmem_set_active is a test-and-set routine, so we only
+	 * arrive here once (since we never disable it)
+	 */
+	mutex_lock(&set_limit_mutex);
+	if ((val != RESOURCE_MAX) && memcg_kmem_set_active(memcg)) {
+
+		mem_cgroup_get(memcg);
+
+		for_each_mem_cgroup_tree(iter, memcg) {
+			if (iter == memcg)
+				continue;
+			memcg_kmem_set_active_parent(iter);
+		}
+	}
+	mutex_unlock(&set_limit_mutex);
+#endif
+}
+
 /*
  * The user of this function is...
  * RES_LIMIT.
@@ -4115,9 +4182,7 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
 			if (ret)
 				break;
 
-			/* For simplicity, we won't allow this to be disabled */
-			if (!memcg->kmem_accounted && val != RESOURCE_MAX)
-				memcg->kmem_accounted = true;
+			memcg_update_kmem_limit(memcg, val);
 		} else
 			return -EINVAL;
 		break;
@@ -4791,6 +4856,20 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
 static void kmem_cgroup_destroy(struct mem_cgroup *memcg)
 {
 	mem_cgroup_sockets_destroy(memcg);
+
+	memcg_kmem_mark_dead(memcg);
+
+	if (res_counter_read_u64(&memcg->kmem, RES_USAGE) != 0)
+		return;
+
+	/*
+	 * Charges already down to 0, undo mem_cgroup_get() done in the charge
+	 * path here, being careful not to race with memcg_uncharge_kmem: it is
+	 * possible that the charges went down to 0 between mark_dead and the
+	 * res_counter read, so in that case, we don't need the put
+	 */
+	if (memcg_kmem_dead(memcg))
+		mem_cgroup_put(memcg);
 }
 #else
 static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
@@ -5148,6 +5227,8 @@ mem_cgroup_create(struct cgroup *cont)
 	}
 
 	if (parent && parent->use_hierarchy) {
+		struct mem_cgroup __maybe_unused *p;
+
 		res_counter_init(&memcg->res, &parent->res);
 		res_counter_init(&memcg->memsw, &parent->memsw);
 		res_counter_init(&memcg->kmem, &parent->kmem);
@@ -5158,6 +5239,20 @@ mem_cgroup_create(struct cgroup *cont)
 		 * mem_cgroup(see mem_cgroup_put).
 		 */
 		mem_cgroup_get(parent);
+#ifdef CONFIG_MEMCG_KMEM
+		/*
+		 * In case a parent is already limited when we create this, we
+		 * need him to propagate it now so we become limited as well.
+		 */
+		mutex_lock(&set_limit_mutex);
+		for (p = parent; p != NULL; p = parent_mem_cgroup(p)) {
+			if (memcg_kmem_is_accounted(p)) {
+				memcg_kmem_set_active_parent(memcg);
+				break;
+			}
+		}
+		mutex_unlock(&set_limit_mutex);
+#endif
 	} else {
 		res_counter_init(&memcg->res, NULL);
 		res_counter_init(&memcg->memsw, NULL);
@@ -5871,9 +5966,15 @@ void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size)
 	if (!memcg)
 		return;
 
-	res_counter_uncharge(&memcg->kmem, size);
 	res_counter_uncharge(&memcg->res, size);
 	if (do_swap_account)
 		res_counter_uncharge(&memcg->memsw, size);
+
+	/* Not down to 0 */
+	if (res_counter_uncharge(&memcg->kmem, size))
+		return;
+
+	if (memcg_kmem_dead(memcg))
+		mem_cgroup_put(memcg);
 }
 #endif /* CONFIG_MEMCG_KMEM */
-- 
1.7.11.4

Re: [PATCH v3 09/13] memcg: kmem accounting lifecycle management

[Michal Hocko]

Based on the previous discussions I guess this one will get reworked,
right?

On Tue 18-09-12 18:04:06, Glauber Costa wrote:
> Because the assignment: memcg->kmem_accounted = true is done after the
> jump labels increment, we guarantee that the root memcg will always be
> selected until all call sites are patched (see memcg_kmem_enabled).
> This guarantees that no mischarges are applied.
> 
> Jump label decrement happens when the last reference count from the
> memcg dies. This will only happen when the caches are all dead.
> 
> -> /cgroups/memory/A/B/C
> 
> * kmem limit set at A,
> * A and B have no tasks,
> * span a new task in in C.
> 
> Because kmem_accounted is a boolean that was not set for C, no
> accounting would be done. This is, however, not what we expect.
> 
> The basic idea, is that when a cgroup is limited, we walk the tree
> downwards and make sure that we store the information about the parent
> being limited in kmem_accounted.
> 
> We do the reverse operation when a formerly limited cgroup becomes
> unlimited.
> 
> Since kmem charges may outlive the cgroup existance, we need to be extra
> careful to guarantee the memcg object will stay around for as long as
> needed. Up to now, we were using a mem_cgroup_get()/put() pair in charge
> and uncharge operations.
> 
> Although this guarantees that the object will be around until the last
> call to unchage, this means an atomic update in every charge. We can do
> better than that if we only issue get() in the first charge, and then
> put() when the last charge finally goes away.
> 
> [ v3: merged all lifecycle related patches in one ]
> 
> Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
> CC: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
> CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
> CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
> CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> CC: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> ---
>  mm/memcontrol.c | 123 +++++++++++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 112 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 0f36a01..720e4bb 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -287,7 +287,8 @@ struct mem_cgroup {
>  	 * Should the accounting and control be hierarchical, per subtree?
>  	 */
>  	bool use_hierarchy;
> -	bool kmem_accounted;
> +
> +	unsigned long kmem_accounted; /* See KMEM_ACCOUNTED_*, below */
>  
>  	bool		oom_lock;
>  	atomic_t	under_oom;
> @@ -340,6 +341,43 @@ struct mem_cgroup {
>  #endif
>  };
>  
> +enum {
> +	KMEM_ACCOUNTED_ACTIVE = 0, /* accounted by this cgroup itself */
> +	KMEM_ACCOUNTED_PARENT, /* one of its parents is active */
> +	KMEM_ACCOUNTED_DEAD, /* dead memcg, pending kmem charges */
> +};
> +
> +/* bits 0 and 1 */
> +#define KMEM_ACCOUNTED_MASK 0x3
> +
> +#ifdef CONFIG_MEMCG_KMEM
> +static bool memcg_kmem_set_active(struct mem_cgroup *memcg)
> +{
> +	return !test_and_set_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_accounted);
> +}
> +
> +static bool memcg_kmem_is_accounted(struct mem_cgroup *memcg)
> +{
> +	return test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_accounted);
> +}
> +
> +static void memcg_kmem_set_active_parent(struct mem_cgroup *memcg)
> +{
> +	set_bit(KMEM_ACCOUNTED_PARENT, &memcg->kmem_accounted);
> +}
> +
> +static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
> +{
> +	if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_accounted))
> +		set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_accounted);
> +}
> +
> +static bool memcg_kmem_dead(struct mem_cgroup *memcg)
> +{
> +	return test_and_clear_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_accounted);
> +}
> +#endif /* CONFIG_MEMCG_KMEM */
> +
>  /* Stuffs for move charges at task migration. */
>  /*
>   * Types of charges to be moved. "move_charge_at_immitgrate" is treated as a
> @@ -491,7 +529,7 @@ EXPORT_SYMBOL(tcp_proto_cgroup);
>  static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
>  {
>  	return !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) &&
> -		memcg->kmem_accounted;
> +		 (memcg->kmem_accounted & (KMEM_ACCOUNTED_MASK));
>  }
>  
>  /*
> @@ -524,13 +562,9 @@ __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
>  	if (!memcg_can_account_kmem(memcg))
>  		return true;
>  
> -	mem_cgroup_get(memcg);
> -
>  	ret = memcg_charge_kmem(memcg, gfp, PAGE_SIZE << order) == 0;
>  	if (ret)
>  		*_memcg = memcg;
> -	else
> -		mem_cgroup_put(memcg);
>  
>  	return ret;
>  }
> @@ -589,7 +623,6 @@ void __memcg_kmem_uncharge_page(struct page *page, int order)
>  
>  	WARN_ON(mem_cgroup_is_root(memcg));
>  	memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
> -	mem_cgroup_put(memcg);
>  }
>  #endif /* CONFIG_MEMCG_KMEM */
>  
> @@ -4077,6 +4110,40 @@ static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
>  	len = scnprintf(str, sizeof(str), "%llu\n", (unsigned long long)val);
>  	return simple_read_from_buffer(buf, nbytes, ppos, str, len);
>  }
> +
> +static void memcg_update_kmem_limit(struct mem_cgroup *memcg, u64 val)
> +{
> +#ifdef CONFIG_MEMCG_KMEM
> +	struct mem_cgroup *iter;
> +
> +	/*
> +	 * When we are doing hierarchical accounting, with an hierarchy like
> +	 * A/B/C, we need to start accounting kernel memory all the way up to C
> +	 * in case A start being accounted.
> +	 *
> +	 * So when we the cgroup first gets to be unlimited, we walk all the
> +	 * children of the current memcg and enable kmem accounting for them.
> +	 * Note that a separate bit is used there to indicate that the
> +	 * accounting happens due to the parent being accounted.
> +	 *
> +	 * note that memcg_kmem_set_active is a test-and-set routine, so we only
> +	 * arrive here once (since we never disable it)
> +	 */
> +	mutex_lock(&set_limit_mutex);
> +	if ((val != RESOURCE_MAX) && memcg_kmem_set_active(memcg)) {
> +
> +		mem_cgroup_get(memcg);
> +
> +		for_each_mem_cgroup_tree(iter, memcg) {
> +			if (iter == memcg)
> +				continue;
> +			memcg_kmem_set_active_parent(iter);
> +		}
> +	}
> +	mutex_unlock(&set_limit_mutex);
> +#endif
> +}
> +
>  /*
>   * The user of this function is...
>   * RES_LIMIT.
> @@ -4115,9 +4182,7 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
>  			if (ret)
>  				break;
>  
> -			/* For simplicity, we won't allow this to be disabled */
> -			if (!memcg->kmem_accounted && val != RESOURCE_MAX)
> -				memcg->kmem_accounted = true;
> +			memcg_update_kmem_limit(memcg, val);
>  		} else
>  			return -EINVAL;
>  		break;
> @@ -4791,6 +4856,20 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
>  static void kmem_cgroup_destroy(struct mem_cgroup *memcg)
>  {
>  	mem_cgroup_sockets_destroy(memcg);
> +
> +	memcg_kmem_mark_dead(memcg);
> +
> +	if (res_counter_read_u64(&memcg->kmem, RES_USAGE) != 0)
> +		return;
> +
> +	/*
> +	 * Charges already down to 0, undo mem_cgroup_get() done in the charge
> +	 * path here, being careful not to race with memcg_uncharge_kmem: it is
> +	 * possible that the charges went down to 0 between mark_dead and the
> +	 * res_counter read, so in that case, we don't need the put
> +	 */
> +	if (memcg_kmem_dead(memcg))
> +		mem_cgroup_put(memcg);
>  }
>  #else
>  static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
> @@ -5148,6 +5227,8 @@ mem_cgroup_create(struct cgroup *cont)
>  	}
>  
>  	if (parent && parent->use_hierarchy) {
> +		struct mem_cgroup __maybe_unused *p;
> +
>  		res_counter_init(&memcg->res, &parent->res);
>  		res_counter_init(&memcg->memsw, &parent->memsw);
>  		res_counter_init(&memcg->kmem, &parent->kmem);
> @@ -5158,6 +5239,20 @@ mem_cgroup_create(struct cgroup *cont)
>  		 * mem_cgroup(see mem_cgroup_put).
>  		 */
>  		mem_cgroup_get(parent);
> +#ifdef CONFIG_MEMCG_KMEM
> +		/*
> +		 * In case a parent is already limited when we create this, we
> +		 * need him to propagate it now so we become limited as well.
> +		 */
> +		mutex_lock(&set_limit_mutex);
> +		for (p = parent; p != NULL; p = parent_mem_cgroup(p)) {
> +			if (memcg_kmem_is_accounted(p)) {
> +				memcg_kmem_set_active_parent(memcg);
> +				break;
> +			}
> +		}
> +		mutex_unlock(&set_limit_mutex);
> +#endif
>  	} else {
>  		res_counter_init(&memcg->res, NULL);
>  		res_counter_init(&memcg->memsw, NULL);
> @@ -5871,9 +5966,15 @@ void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size)
>  	if (!memcg)
>  		return;
>  
> -	res_counter_uncharge(&memcg->kmem, size);
>  	res_counter_uncharge(&memcg->res, size);
>  	if (do_swap_account)
>  		res_counter_uncharge(&memcg->memsw, size);
> +
> +	/* Not down to 0 */
> +	if (res_counter_uncharge(&memcg->kmem, size))
> +		return;
> +
> +	if (memcg_kmem_dead(memcg))
> +		mem_cgroup_put(memcg);
>  }
>  #endif /* CONFIG_MEMCG_KMEM */
> -- 
> 1.7.11.4
> 
> --
> To unsubscribe from this list: send the line "unsubscribe cgroups" in
> the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 09/13] memcg: kmem accounting lifecycle management

[Glauber Costa]

On 10/01/2012 04:15 PM, Michal Hocko wrote:
> Based on the previous discussions I guess this one will get reworked,
> right?
> 

Yes, but most of it stayed. The hierarchy part is gone, but because we
will still have kmem pages floating around (potentially), I am still
using the mark_dead() trick with the corresponding get when kmem_accounted.

Re: [PATCH v3 09/13] memcg: kmem accounting lifecycle management

[Michal Hocko]

On Mon 01-10-12 16:29:11, Glauber Costa wrote:
> On 10/01/2012 04:15 PM, Michal Hocko wrote:
> > Based on the previous discussions I guess this one will get reworked,
> > right?
> > 
> 
> Yes, but most of it stayed. The hierarchy part is gone, but because we
> will still have kmem pages floating around (potentially), I am still
> using the mark_dead() trick with the corresponding get when kmem_accounted.

Is it OK if I hold on with the review of this one until the next
version?
-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 09/13] memcg: kmem accounting lifecycle management

[Glauber Costa]

On 10/01/2012 04:36 PM, Michal Hocko wrote:
> On Mon 01-10-12 16:29:11, Glauber Costa wrote:
>> On 10/01/2012 04:15 PM, Michal Hocko wrote:
>>> Based on the previous discussions I guess this one will get reworked,
>>> right?
>>>
>>
>> Yes, but most of it stayed. The hierarchy part is gone, but because we
>> will still have kmem pages floating around (potentially), I am still
>> using the mark_dead() trick with the corresponding get when kmem_accounted.
> 
> Is it OK if I hold on with the review of this one until the next
> version?
> 
Of course.

I haven't sent it yet because I also received a lot more feedback for
the slab part (which is expected), and I want to get a least part of
that going before I send it again.

[PATCH v3 10/13] memcg: use static branches when code not in use

[Glauber Costa]

We can use static branches to patch the code in or out when not used.

Because the _ACTIVATED bit on kmem_accounted is only set once, we
guarantee that the root memcg will always be selected until all call
sites are patched (see memcg_kmem_enabled).  This guarantees that no
mischarges are applied.

static branch decrement happens when the last reference count from the
kmem accounting in memcg dies. This will only happen when the charges
drop down to 0.

Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
CC: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
CC: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
---
 include/linux/memcontrol.h |  4 +++-
 mm/memcontrol.c            | 26 ++++++++++++++++++++++++--
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 82ede9a..4ec9fd5 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -22,6 +22,7 @@
 #include <linux/cgroup.h>
 #include <linux/vm_event_item.h>
 #include <linux/hardirq.h>
+#include <linux/jump_label.h>
 
 struct mem_cgroup;
 struct page_cgroup;
@@ -401,9 +402,10 @@ struct sock;
 void sock_update_memcg(struct sock *sk);
 void sock_release_memcg(struct sock *sk);
 
+extern struct static_key memcg_kmem_enabled_key;
 static inline bool memcg_kmem_enabled(void)
 {
-	return true;
+	return static_key_false(&memcg_kmem_enabled_key);
 }
 
 extern bool __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 720e4bb..aada601 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -467,6 +467,8 @@ struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
 #include <net/sock.h>
 #include <net/ip.h>
 
+struct static_key memcg_kmem_enabled_key;
+
 static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
 static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size);
 static void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size);
@@ -624,6 +626,16 @@ void __memcg_kmem_uncharge_page(struct page *page, int order)
 	WARN_ON(mem_cgroup_is_root(memcg));
 	memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
 }
+
+static void disarm_kmem_keys(struct mem_cgroup *memcg)
+{
+	if (memcg_kmem_is_accounted(memcg))
+		static_key_slow_dec(&memcg_kmem_enabled_key);
+}
+#else
+static void disarm_kmem_keys(struct mem_cgroup *memcg)
+{
+}
 #endif /* CONFIG_MEMCG_KMEM */
 
 #if defined(CONFIG_INET) && defined(CONFIG_MEMCG_KMEM)
@@ -639,6 +651,12 @@ static void disarm_sock_keys(struct mem_cgroup *memcg)
 }
 #endif
 
+static void disarm_static_keys(struct mem_cgroup *memcg)
+{
+	disarm_sock_keys(memcg);
+	disarm_kmem_keys(memcg);
+}
+
 static void drain_all_stock_async(struct mem_cgroup *memcg);
 
 static struct mem_cgroup_per_zone *
@@ -4131,7 +4149,11 @@ static void memcg_update_kmem_limit(struct mem_cgroup *memcg, u64 val)
 	 */
 	mutex_lock(&set_limit_mutex);
 	if ((val != RESOURCE_MAX) && memcg_kmem_set_active(memcg)) {
-
+		/*
+		 * Once the static branch is enabled it will only be
+		 * disabled when the last reference to memcg is gone.
+		 */
+		static_key_slow_inc(&memcg_kmem_enabled_key);
 		mem_cgroup_get(memcg);
 
 		for_each_mem_cgroup_tree(iter, memcg) {
@@ -5066,7 +5088,7 @@ static void free_work(struct work_struct *work)
 	 * to move this code around, and make sure it is outside
 	 * the cgroup_lock.
 	 */
-	disarm_sock_keys(memcg);
+	disarm_static_keys(memcg);
 	if (size < PAGE_SIZE)
 		kfree(memcg);
 	else
-- 
1.7.11.4

Re: [PATCH v3 10/13] memcg: use static branches when code not in use

[Michal Hocko]

On Tue 18-09-12 18:04:07, Glauber Costa wrote:
[...]
>  include/linux/memcontrol.h |  4 +++-
>  mm/memcontrol.c            | 26 ++++++++++++++++++++++++--
>  2 files changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 82ede9a..4ec9fd5 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -22,6 +22,7 @@
>  #include <linux/cgroup.h>
>  #include <linux/vm_event_item.h>
>  #include <linux/hardirq.h>
> +#include <linux/jump_label.h>
>  
>  struct mem_cgroup;
>  struct page_cgroup;
> @@ -401,9 +402,10 @@ struct sock;
>  void sock_update_memcg(struct sock *sk);
>  void sock_release_memcg(struct sock *sk);
>  
> +extern struct static_key memcg_kmem_enabled_key;
>  static inline bool memcg_kmem_enabled(void)
>  {
> -	return true;
> +	return static_key_false(&memcg_kmem_enabled_key);
>  }
>  
>  extern bool __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg,
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 720e4bb..aada601 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -467,6 +467,8 @@ struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
>  #include <net/sock.h>
>  #include <net/ip.h>
>  
> +struct static_key memcg_kmem_enabled_key;
> +
>  static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
>  static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size);
>  static void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size);
> @@ -624,6 +626,16 @@ void __memcg_kmem_uncharge_page(struct page *page, int order)
>  	WARN_ON(mem_cgroup_is_root(memcg));
>  	memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
>  }
> +
> +static void disarm_kmem_keys(struct mem_cgroup *memcg)
> +{
> +	if (memcg_kmem_is_accounted(memcg))
> +		static_key_slow_dec(&memcg_kmem_enabled_key);
> +}
> +#else
> +static void disarm_kmem_keys(struct mem_cgroup *memcg)
> +{
> +}
>  #endif /* CONFIG_MEMCG_KMEM */
>  
>  #if defined(CONFIG_INET) && defined(CONFIG_MEMCG_KMEM)
> @@ -639,6 +651,12 @@ static void disarm_sock_keys(struct mem_cgroup *memcg)
>  }
>  #endif
>  
> +static void disarm_static_keys(struct mem_cgroup *memcg)
> +{
> +	disarm_sock_keys(memcg);
> +	disarm_kmem_keys(memcg);
> +}
> +
>  static void drain_all_stock_async(struct mem_cgroup *memcg);
>  
>  static struct mem_cgroup_per_zone *
> @@ -4131,7 +4149,11 @@ static void memcg_update_kmem_limit(struct mem_cgroup *memcg, u64 val)
>  	 */
>  	mutex_lock(&set_limit_mutex);
>  	if ((val != RESOURCE_MAX) && memcg_kmem_set_active(memcg)) {
> -
> +		/*
> +		 * Once the static branch is enabled it will only be
> +		 * disabled when the last reference to memcg is gone.
> +		 */
> +		static_key_slow_inc(&memcg_kmem_enabled_key);

I guess the reason why we do not need to inc also for children is that
we do not inherit kmem_accounted, right?

>  		mem_cgroup_get(memcg);
>  
>  		for_each_mem_cgroup_tree(iter, memcg) {
> @@ -5066,7 +5088,7 @@ static void free_work(struct work_struct *work)
>  	 * to move this code around, and make sure it is outside
>  	 * the cgroup_lock.
>  	 */
> -	disarm_sock_keys(memcg);
> +	disarm_static_keys(memcg);
>  	if (size < PAGE_SIZE)
>  		kfree(memcg);
>  	else
> -- 
> 1.7.11.4
> 
> --
> To unsubscribe from this list: send the line "unsubscribe cgroups" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Michal Hocko
SUSE Labs

--
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Re: [PATCH v3 10/13] memcg: use static branches when code not in use

[Glauber Costa]

On 10/01/2012 04:25 PM, Michal Hocko wrote:
> On Tue 18-09-12 18:04:07, Glauber Costa wrote:
> [...]
>>  include/linux/memcontrol.h |  4 +++-
>>  mm/memcontrol.c            | 26 ++++++++++++++++++++++++--
>>  2 files changed, 27 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index 82ede9a..4ec9fd5 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -22,6 +22,7 @@
>>  #include <linux/cgroup.h>
>>  #include <linux/vm_event_item.h>
>>  #include <linux/hardirq.h>
>> +#include <linux/jump_label.h>
>>  
>>  struct mem_cgroup;
>>  struct page_cgroup;
>> @@ -401,9 +402,10 @@ struct sock;
>>  void sock_update_memcg(struct sock *sk);
>>  void sock_release_memcg(struct sock *sk);
>>  
>> +extern struct static_key memcg_kmem_enabled_key;
>>  static inline bool memcg_kmem_enabled(void)
>>  {
>> -	return true;
>> +	return static_key_false(&memcg_kmem_enabled_key);
>>  }
>>  
>>  extern bool __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg,
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 720e4bb..aada601 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -467,6 +467,8 @@ struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
>>  #include <net/sock.h>
>>  #include <net/ip.h>
>>  
>> +struct static_key memcg_kmem_enabled_key;
>> +
>>  static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
>>  static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size);
>>  static void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size);
>> @@ -624,6 +626,16 @@ void __memcg_kmem_uncharge_page(struct page *page, int order)
>>  	WARN_ON(mem_cgroup_is_root(memcg));
>>  	memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
>>  }
>> +
>> +static void disarm_kmem_keys(struct mem_cgroup *memcg)
>> +{
>> +	if (memcg_kmem_is_accounted(memcg))
>> +		static_key_slow_dec(&memcg_kmem_enabled_key);
>> +}
>> +#else
>> +static void disarm_kmem_keys(struct mem_cgroup *memcg)
>> +{
>> +}
>>  #endif /* CONFIG_MEMCG_KMEM */
>>  
>>  #if defined(CONFIG_INET) && defined(CONFIG_MEMCG_KMEM)
>> @@ -639,6 +651,12 @@ static void disarm_sock_keys(struct mem_cgroup *memcg)
>>  }
>>  #endif
>>  
>> +static void disarm_static_keys(struct mem_cgroup *memcg)
>> +{
>> +	disarm_sock_keys(memcg);
>> +	disarm_kmem_keys(memcg);
>> +}
>> +
>>  static void drain_all_stock_async(struct mem_cgroup *memcg);
>>  
>>  static struct mem_cgroup_per_zone *
>> @@ -4131,7 +4149,11 @@ static void memcg_update_kmem_limit(struct mem_cgroup *memcg, u64 val)
>>  	 */
>>  	mutex_lock(&set_limit_mutex);
>>  	if ((val != RESOURCE_MAX) && memcg_kmem_set_active(memcg)) {
>> -
>> +		/*
>> +		 * Once the static branch is enabled it will only be
>> +		 * disabled when the last reference to memcg is gone.
>> +		 */
>> +		static_key_slow_inc(&memcg_kmem_enabled_key);
> 
> I guess the reason why we do not need to inc also for children is that
> we do not inherit kmem_accounted, right?
> 

Yes, but I of course changed that in the upcoming version of the patch.
We now inherit the value everytime, and the static branches are updated
accordingly.

[PATCH v3 11/13] memcg: allow a memcg with kmem charges to be destructed.

[Glauber Costa]

Because the ultimate goal of the kmem tracking in memcg is to track slab
pages as well, we can't guarantee that we'll always be able to point a
page to a particular process, and migrate the charges along with it -
since in the common case, a page will contain data belonging to multiple
processes.

Because of that, when we destroy a memcg, we only make sure the
destruction will succeed by discounting the kmem charges from the user
charges when we try to empty the cgroup.

Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
CC: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
CC: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
---
 mm/memcontrol.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index aada601..b05ecac 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -631,6 +631,11 @@ static void disarm_kmem_keys(struct mem_cgroup *memcg)
 {
 	if (memcg_kmem_is_accounted(memcg))
 		static_key_slow_dec(&memcg_kmem_enabled_key);
+	/*
+	 * This check can't live in kmem destruction function,
+	 * since the charges will outlive the cgroup
+	 */
+	WARN_ON(res_counter_read_u64(&memcg->kmem, RES_USAGE) != 0);
 }
 #else
 static void disarm_kmem_keys(struct mem_cgroup *memcg)
@@ -3933,6 +3938,7 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg, bool free_all)
 	int node, zid, shrink;
 	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
 	struct cgroup *cgrp = memcg->css.cgroup;
+	u64 usage;
 
 	css_get(&memcg->css);
 
@@ -3966,8 +3972,17 @@ move_account:
 		mem_cgroup_end_move(memcg);
 		memcg_oom_recover(memcg);
 		cond_resched();
+		/*
+		 * Kernel memory may not necessarily be trackable to a specific
+		 * process. So they are not migrated, and therefore we can't
+		 * expect their value to drop to 0 here.
+		 *
+		 * having res filled up with kmem only is enough
+		 */
+		usage = res_counter_read_u64(&memcg->res, RES_USAGE) -
+			res_counter_read_u64(&memcg->kmem, RES_USAGE);
 	/* "ret" should also be checked to ensure all lists are empty. */
-	} while (res_counter_read_u64(&memcg->res, RES_USAGE) > 0 || ret);
+	} while (usage > 0 || ret);
 out:
 	css_put(&memcg->css);
 	return ret;
-- 
1.7.11.4

Re: [PATCH v3 11/13] memcg: allow a memcg with kmem charges to be destructed.

[Michal Hocko]

On Tue 18-09-12 18:04:08, Glauber Costa wrote:
> Because the ultimate goal of the kmem tracking in memcg is to track slab
> pages as well, we can't guarantee that we'll always be able to point a
> page to a particular process, and migrate the charges along with it -
> since in the common case, a page will contain data belonging to multiple
> processes.
> 
> Because of that, when we destroy a memcg, we only make sure the
> destruction will succeed by discounting the kmem charges from the user
> charges when we try to empty the cgroup.
> 
> Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
> CC: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
> CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
> CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
> CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> CC: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>

Looks good.
Reviewed-by: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>

> ---
>  mm/memcontrol.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index aada601..b05ecac 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -631,6 +631,11 @@ static void disarm_kmem_keys(struct mem_cgroup *memcg)
>  {
>  	if (memcg_kmem_is_accounted(memcg))
>  		static_key_slow_dec(&memcg_kmem_enabled_key);
> +	/*
> +	 * This check can't live in kmem destruction function,
> +	 * since the charges will outlive the cgroup
> +	 */
> +	WARN_ON(res_counter_read_u64(&memcg->kmem, RES_USAGE) != 0);
>  }
>  #else
>  static void disarm_kmem_keys(struct mem_cgroup *memcg)
> @@ -3933,6 +3938,7 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg, bool free_all)
>  	int node, zid, shrink;
>  	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
>  	struct cgroup *cgrp = memcg->css.cgroup;
> +	u64 usage;
>  
>  	css_get(&memcg->css);
>  
> @@ -3966,8 +3972,17 @@ move_account:
>  		mem_cgroup_end_move(memcg);
>  		memcg_oom_recover(memcg);
>  		cond_resched();
> +		/*
> +		 * Kernel memory may not necessarily be trackable to a specific
> +		 * process. So they are not migrated, and therefore we can't
> +		 * expect their value to drop to 0 here.
> +		 *
> +		 * having res filled up with kmem only is enough
> +		 */
> +		usage = res_counter_read_u64(&memcg->res, RES_USAGE) -
> +			res_counter_read_u64(&memcg->kmem, RES_USAGE);
>  	/* "ret" should also be checked to ensure all lists are empty. */
> -	} while (res_counter_read_u64(&memcg->res, RES_USAGE) > 0 || ret);
> +	} while (usage > 0 || ret);
>  out:
>  	css_put(&memcg->css);
>  	return ret;
> -- 
> 1.7.11.4
> 
> --
> To unsubscribe from this list: send the line "unsubscribe cgroups" in
> the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Michal Hocko
SUSE Labs

[PATCH v3 12/13] execute the whole memcg freeing in rcu callback

[Glauber Costa]

A lot of the initialization we do in mem_cgroup_create() is done with softirqs
enabled. This include grabbing a css id, which holds &ss->id_lock->rlock, and
the per-zone trees, which holds rtpz->lock->rlock. All of those signal to the
lockdep mechanism that those locks can be used in SOFTIRQ-ON-W context. This
means that the freeing of memcg structure must happen in a compatible context,
otherwise we'll get a deadlock.

The reference counting mechanism we use allows the memcg structure to be freed
later and outlive the actual memcg destruction from the filesystem. However, we
have little, if any, means to guarantee in which context the last memcg_put
will happen. The best we can do is test it and try to make sure no invalid
context releases are happening. But as we add more code to memcg, the possible
interactions grow in number and expose more ways to get context conflicts.

We already moved a part of the freeing to a worker thread to be context-safe
for the static branches disabling. I see no reason not to do it for the whole
freeing action. I consider this to be the safe choice.

Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
Tested-by: Greg Thelen <gthelen-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
---
 mm/memcontrol.c | 66 +++++++++++++++++++++++++++++----------------------------
 1 file changed, 34 insertions(+), 32 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b05ecac..74654f0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5082,16 +5082,29 @@ out_free:
 }
 
 /*
- * Helpers for freeing a kmalloc()ed/vzalloc()ed mem_cgroup by RCU,
- * but in process context.  The work_freeing structure is overlaid
- * on the rcu_freeing structure, which itself is overlaid on memsw.
+ * At destroying mem_cgroup, references from swap_cgroup can remain.
+ * (scanning all at force_empty is too costly...)
+ *
+ * Instead of clearing all references at force_empty, we remember
+ * the number of reference from swap_cgroup and free mem_cgroup when
+ * it goes down to 0.
+ *
+ * Removal of cgroup itself succeeds regardless of refs from swap.
  */
-static void free_work(struct work_struct *work)
+
+static void __mem_cgroup_free(struct mem_cgroup *memcg)
 {
-	struct mem_cgroup *memcg;
+	int node;
 	int size = sizeof(struct mem_cgroup);
 
-	memcg = container_of(work, struct mem_cgroup, work_freeing);
+	mem_cgroup_remove_from_trees(memcg);
+	free_css_id(&mem_cgroup_subsys, &memcg->css);
+
+	for_each_node(node)
+		free_mem_cgroup_per_zone_info(memcg, node);
+
+	free_percpu(memcg->stat);
+
 	/*
 	 * We need to make sure that (at least for now), the jump label
 	 * destruction code runs outside of the cgroup lock. This is because
@@ -5110,38 +5123,27 @@ static void free_work(struct work_struct *work)
 		vfree(memcg);
 }
 
-static void free_rcu(struct rcu_head *rcu_head)
-{
-	struct mem_cgroup *memcg;
-
-	memcg = container_of(rcu_head, struct mem_cgroup, rcu_freeing);
-	INIT_WORK(&memcg->work_freeing, free_work);
-	schedule_work(&memcg->work_freeing);
-}
 
 /*
- * At destroying mem_cgroup, references from swap_cgroup can remain.
- * (scanning all at force_empty is too costly...)
- *
- * Instead of clearing all references at force_empty, we remember
- * the number of reference from swap_cgroup and free mem_cgroup when
- * it goes down to 0.
- *
- * Removal of cgroup itself succeeds regardless of refs from swap.
+ * Helpers for freeing a kmalloc()ed/vzalloc()ed mem_cgroup by RCU,
+ * but in process context.  The work_freeing structure is overlaid
+ * on the rcu_freeing structure, which itself is overlaid on memsw.
  */
-
-static void __mem_cgroup_free(struct mem_cgroup *memcg)
+static void free_work(struct work_struct *work)
 {
-	int node;
+	struct mem_cgroup *memcg;
 
-	mem_cgroup_remove_from_trees(memcg);
-	free_css_id(&mem_cgroup_subsys, &memcg->css);
+	memcg = container_of(work, struct mem_cgroup, work_freeing);
+	__mem_cgroup_free(memcg);
+}
 
-	for_each_node(node)
-		free_mem_cgroup_per_zone_info(memcg, node);
+static void free_rcu(struct rcu_head *rcu_head)
+{
+	struct mem_cgroup *memcg;
 
-	free_percpu(memcg->stat);
-	call_rcu(&memcg->rcu_freeing, free_rcu);
+	memcg = container_of(rcu_head, struct mem_cgroup, rcu_freeing);
+	INIT_WORK(&memcg->work_freeing, free_work);
+	schedule_work(&memcg->work_freeing);
 }
 
 static void mem_cgroup_get(struct mem_cgroup *memcg)
@@ -5153,7 +5155,7 @@ static void __mem_cgroup_put(struct mem_cgroup *memcg, int count)
 {
 	if (atomic_sub_and_test(count, &memcg->refcnt)) {
 		struct mem_cgroup *parent = parent_mem_cgroup(memcg);
-		__mem_cgroup_free(memcg);
+		call_rcu(&memcg->rcu_freeing, free_rcu);
 		if (parent)
 			mem_cgroup_put(parent);
 	}
-- 
1.7.11.4

Re: [PATCH v3 12/13] execute the whole memcg freeing in rcu callback

[Tejun Heo]

Hello, Glauber.

On Tue, Sep 18, 2012 at 06:04:09PM +0400, Glauber Costa wrote:
> A lot of the initialization we do in mem_cgroup_create() is done with softirqs
> enabled. This include grabbing a css id, which holds &ss->id_lock->rlock, and
> the per-zone trees, which holds rtpz->lock->rlock. All of those signal to the
> lockdep mechanism that those locks can be used in SOFTIRQ-ON-W context. This
> means that the freeing of memcg structure must happen in a compatible context,
> otherwise we'll get a deadlock.

Lockdep requires lock to be softirq or irq safe iff the lock is
actually acquired from the said context.  Merely using a lock with bh
/ irq disabled doesn't signal that to lockdep; otherwise, we'll end up
with enormous number of spurious warnings.

> The reference counting mechanism we use allows the memcg structure to be freed
> later and outlive the actual memcg destruction from the filesystem. However, we
> have little, if any, means to guarantee in which context the last memcg_put
> will happen. The best we can do is test it and try to make sure no invalid
> context releases are happening. But as we add more code to memcg, the possible
> interactions grow in number and expose more ways to get context conflicts.
> 
> We already moved a part of the freeing to a worker thread to be context-safe
> for the static branches disabling. I see no reason not to do it for the whole
> freeing action. I consider this to be the safe choice.

And the above description too makes me scratch my head quite a bit.  I
can see what the patch is doing but can't understand the why.

* Why was it punting the freeing to workqueue anyway?  ISTR something
  about static_keys but my memory fails.  What changed?  Why don't we
  need it anymore?

* As for locking context, the above description seems a bit misleading
  to me.  Synchronization constructs involved there currently doesn't
  require softirq or irq safe context.  If that needs to change,
  that's fine but that's a completely different reason than given
  above.

Thanks.

-- 
tejun

Re: [PATCH v3 12/13] execute the whole memcg freeing in rcu callback

[Glauber Costa]

> And the above description too makes me scratch my head quite a bit.  I
> can see what the patch is doing but can't understand the why.
> 
> * Why was it punting the freeing to workqueue anyway?  ISTR something
>   about static_keys but my memory fails.  What changed?  Why don't we
>   need it anymore?
> 
> * As for locking context, the above description seems a bit misleading
>   to me.  Synchronization constructs involved there currently doesn't
>   require softirq or irq safe context.  If that needs to change,
>   that's fine but that's a completely different reason than given
>   above.
> 
> Thanks.
> 

I just suck at changelogs =(

The problem here is very much like the one we had with static branches.
In that case, we had the problem with the cgroup_lock() being held, in
which case the jump label lock could not be called.

In here, after the kmem patches are in, the destruction function could
be called directly from memcg_kmem_uncharge_page() when the last put is
done. But this can actually be called from the page allocator, with an
incompatible softirq context. So it is not that it could be called, they
are actually called in that context at this point.

Re: [PATCH v3 12/13] execute the whole memcg freeing in rcu callback

[Michal Hocko]

On Tue 18-09-12 18:04:09, Glauber Costa wrote:
> A lot of the initialization we do in mem_cgroup_create() is done with softirqs
> enabled. This include grabbing a css id, which holds &ss->id_lock->rlock, and
> the per-zone trees, which holds rtpz->lock->rlock. All of those signal to the
> lockdep mechanism that those locks can be used in SOFTIRQ-ON-W context. This
> means that the freeing of memcg structure must happen in a compatible context,
> otherwise we'll get a deadlock.

Maybe I am missing something obvious but why cannot we simply disble
(soft)irqs in mem_cgroup_create rather than make the free path much more
complicated. It really feels strange to defer everything (e.g. soft
reclaim tree cleanup which should be a no-op at the time because there
shouldn't be any user pages in the group).

> The reference counting mechanism we use allows the memcg structure to be freed
> later and outlive the actual memcg destruction from the filesystem. However, we
> have little, if any, means to guarantee in which context the last memcg_put
> will happen. The best we can do is test it and try to make sure no invalid
> context releases are happening. But as we add more code to memcg, the possible
> interactions grow in number and expose more ways to get context conflicts.
> 
> We already moved a part of the freeing to a worker thread to be context-safe
> for the static branches disabling. I see no reason not to do it for the whole
> freeing action. I consider this to be the safe choice.


> 
> Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
> Tested-by: Greg Thelen <gthelen-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
> CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
> CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> ---
>  mm/memcontrol.c | 66 +++++++++++++++++++++++++++++----------------------------
>  1 file changed, 34 insertions(+), 32 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b05ecac..74654f0 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5082,16 +5082,29 @@ out_free:
>  }
>  
>  /*
> - * Helpers for freeing a kmalloc()ed/vzalloc()ed mem_cgroup by RCU,
> - * but in process context.  The work_freeing structure is overlaid
> - * on the rcu_freeing structure, which itself is overlaid on memsw.
> + * At destroying mem_cgroup, references from swap_cgroup can remain.
> + * (scanning all at force_empty is too costly...)
> + *
> + * Instead of clearing all references at force_empty, we remember
> + * the number of reference from swap_cgroup and free mem_cgroup when
> + * it goes down to 0.
> + *
> + * Removal of cgroup itself succeeds regardless of refs from swap.
>   */
> -static void free_work(struct work_struct *work)
> +
> +static void __mem_cgroup_free(struct mem_cgroup *memcg)
>  {
> -	struct mem_cgroup *memcg;
> +	int node;
>  	int size = sizeof(struct mem_cgroup);
>  
> -	memcg = container_of(work, struct mem_cgroup, work_freeing);
> +	mem_cgroup_remove_from_trees(memcg);
> +	free_css_id(&mem_cgroup_subsys, &memcg->css);
> +
> +	for_each_node(node)
> +		free_mem_cgroup_per_zone_info(memcg, node);
> +
> +	free_percpu(memcg->stat);
> +
>  	/*
>  	 * We need to make sure that (at least for now), the jump label
>  	 * destruction code runs outside of the cgroup lock. This is because
> @@ -5110,38 +5123,27 @@ static void free_work(struct work_struct *work)
>  		vfree(memcg);
>  }
>  
> -static void free_rcu(struct rcu_head *rcu_head)
> -{
> -	struct mem_cgroup *memcg;
> -
> -	memcg = container_of(rcu_head, struct mem_cgroup, rcu_freeing);
> -	INIT_WORK(&memcg->work_freeing, free_work);
> -	schedule_work(&memcg->work_freeing);
> -}
>  
>  /*
> - * At destroying mem_cgroup, references from swap_cgroup can remain.
> - * (scanning all at force_empty is too costly...)
> - *
> - * Instead of clearing all references at force_empty, we remember
> - * the number of reference from swap_cgroup and free mem_cgroup when
> - * it goes down to 0.
> - *
> - * Removal of cgroup itself succeeds regardless of refs from swap.
> + * Helpers for freeing a kmalloc()ed/vzalloc()ed mem_cgroup by RCU,
> + * but in process context.  The work_freeing structure is overlaid
> + * on the rcu_freeing structure, which itself is overlaid on memsw.
>   */
> -
> -static void __mem_cgroup_free(struct mem_cgroup *memcg)
> +static void free_work(struct work_struct *work)
>  {
> -	int node;
> +	struct mem_cgroup *memcg;
>  
> -	mem_cgroup_remove_from_trees(memcg);
> -	free_css_id(&mem_cgroup_subsys, &memcg->css);
> +	memcg = container_of(work, struct mem_cgroup, work_freeing);
> +	__mem_cgroup_free(memcg);
> +}
>  
> -	for_each_node(node)
> -		free_mem_cgroup_per_zone_info(memcg, node);
> +static void free_rcu(struct rcu_head *rcu_head)
> +{
> +	struct mem_cgroup *memcg;
>  
> -	free_percpu(memcg->stat);
> -	call_rcu(&memcg->rcu_freeing, free_rcu);
> +	memcg = container_of(rcu_head, struct mem_cgroup, rcu_freeing);
> +	INIT_WORK(&memcg->work_freeing, free_work);
> +	schedule_work(&memcg->work_freeing);
>  }
>  
>  static void mem_cgroup_get(struct mem_cgroup *memcg)
> @@ -5153,7 +5155,7 @@ static void __mem_cgroup_put(struct mem_cgroup *memcg, int count)
>  {
>  	if (atomic_sub_and_test(count, &memcg->refcnt)) {
>  		struct mem_cgroup *parent = parent_mem_cgroup(memcg);
> -		__mem_cgroup_free(memcg);
> +		call_rcu(&memcg->rcu_freeing, free_rcu);
>  		if (parent)
>  			mem_cgroup_put(parent);
>  	}
> -- 
> 1.7.11.4
> 
> --
> To unsubscribe from this list: send the line "unsubscribe cgroups" in
> the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Michal Hocko
SUSE Labs

Re: [PATCH v3 12/13] execute the whole memcg freeing in rcu callback

[Glauber Costa]

On 10/01/2012 05:27 PM, Michal Hocko wrote:
> On Tue 18-09-12 18:04:09, Glauber Costa wrote:
>> A lot of the initialization we do in mem_cgroup_create() is done with softirqs
>> enabled. This include grabbing a css id, which holds &ss->id_lock->rlock, and
>> the per-zone trees, which holds rtpz->lock->rlock. All of those signal to the
>> lockdep mechanism that those locks can be used in SOFTIRQ-ON-W context. This
>> means that the freeing of memcg structure must happen in a compatible context,
>> otherwise we'll get a deadlock.
> 
> Maybe I am missing something obvious but why cannot we simply disble
> (soft)irqs in mem_cgroup_create rather than make the free path much more
> complicated. It really feels strange to defer everything (e.g. soft
> reclaim tree cleanup which should be a no-op at the time because there
> shouldn't be any user pages in the group).
> 

Ok.

I was just able to come back to this today - I was mostly working on the
slab feedback over the past few days. I will answer yours and Tejun's
concerns at once:

Here is the situation: the backtrace I get is this one:

[  124.956725] =================================
[  124.957217] [ INFO: inconsistent lock state ]
[  124.957217] 3.5.0+ #99 Not tainted
[  124.957217] ---------------------------------
[  124.957217] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
[  124.957217] ksoftirqd/0/3 [HC0[0]:SC1[1]:HE1:SE0] takes:
[  124.957217]  (&(&ss->id_lock)->rlock){+.?...}, at:
[<ffffffff810aa7b2>] spin_lock+0x9/0xb
[  124.957217] {SOFTIRQ-ON-W} state was registered at:
[  124.957217]   [<ffffffff810996ed>] __lock_acquire+0x31f/0xd68
[  124.957217]   [<ffffffff8109a660>] lock_acquire+0x108/0x15c
[  124.957217]   [<ffffffff81534ec4>] _raw_spin_lock+0x40/0x4f
[  124.957217]   [<ffffffff810aa7b2>] spin_lock+0x9/0xb
[  124.957217]   [<ffffffff810ad00e>] get_new_cssid+0x69/0xf3
[  124.957217]   [<ffffffff810ad0da>] cgroup_init_idr+0x42/0x60
[  124.957217]   [<ffffffff81b20e04>] cgroup_init+0x50/0x100
[  124.957217]   [<ffffffff81b05b9b>] start_kernel+0x3b9/0x3ee
[  124.957217]   [<ffffffff81b052d6>] x86_64_start_reservations+0xb1/0xb5
[  124.957217]   [<ffffffff81b053d8>] x86_64_start_kernel+0xfe/0x10b


So what we learn from it, is: we are acquiring a specific lock (the css
id one) from softirq context. It was previously taken in a
softirq-enabled context, that seems to be coming directly from
get_new_cssid.

Tejun correctly pointed out that we should never acquire that lock from
a softirq context, in which he is right.

But the situation changes slightly with kmem. Now, the following excerpt
of a backtrace is possible:

[   48.602775]  [<ffffffff81103095>] free_accounted_pages+0x47/0x4c
[   48.602775]  [<ffffffff81047f90>] free_task+0x31/0x5c
[   48.602775]  [<ffffffff8104807d>] __put_task_struct+0xc2/0xdb
[   48.602775]  [<ffffffff8104dfc7>] put_task_struct+0x1e/0x22
[   48.602775]  [<ffffffff8104e144>] delayed_put_task_struct+0x7a/0x98
[   48.602775]  [<ffffffff810cf0e5>] __rcu_process_callbacks+0x269/0x3df
[   48.602775]  [<ffffffff810cf28c>] rcu_process_callbacks+0x31/0x5b
[   48.602775]  [<ffffffff8105266d>] __do_softirq+0x122/0x277

So as you can see, free_accounted_pages (that will trigger a memcg_put()
-> mem_cgroup_free()) can now be called from softirq context, which is,
an rcu callback (and I just realized I wrote the exact opposite in the
subj line: man, I really suck at that!!)
As a matter of fact, we could not move to our rcu callback as well:

we need to move it to a worker thread with the rest.

We already have a worker thread: he reason we have it is not
static_branches: The reason is vfree(), that will BUG_ON(in_interrupt())
and could not be called from rcu callback as well. We moved static
branches in there as well for a similar problem, but haven't introduced it.

Could we move just part of it to the worker thread? Absolutely yes.
Moving just free_css_id() is enough to make it work. But since it is not
the first context related problem we had, I thought: "to hell with that,
let's move everything and be safe".

I am fine moving free_css_id() only if you would prefer.

Can we disable softirqs when we initialize css_id? Maybe. My machine
seems to boot fine and survive the simple workload that would trigger
that bug if I use irqsave spinlocks instead of normal spinlocks. But
this has to be done from cgroup core: We have no control over css
creation in memcg.

How would you guys like me to handle this ?

Re: [PATCH v3 12/13] execute the whole memcg freeing in rcu callback

[Glauber Costa]

On 10/04/2012 02:53 PM, Glauber Costa wrote:
> On 10/01/2012 05:27 PM, Michal Hocko wrote:
>> On Tue 18-09-12 18:04:09, Glauber Costa wrote:
>>> A lot of the initialization we do in mem_cgroup_create() is done with softirqs
>>> enabled. This include grabbing a css id, which holds &ss->id_lock->rlock, and
>>> the per-zone trees, which holds rtpz->lock->rlock. All of those signal to the
>>> lockdep mechanism that those locks can be used in SOFTIRQ-ON-W context. This
>>> means that the freeing of memcg structure must happen in a compatible context,
>>> otherwise we'll get a deadlock.
>>
>> Maybe I am missing something obvious but why cannot we simply disble
>> (soft)irqs in mem_cgroup_create rather than make the free path much more
>> complicated. It really feels strange to defer everything (e.g. soft
>> reclaim tree cleanup which should be a no-op at the time because there
>> shouldn't be any user pages in the group).
>>
> 
> Ok.
> 
> I was just able to come back to this today - I was mostly working on the
> slab feedback over the past few days. I will answer yours and Tejun's
> concerns at once:
> 
> Here is the situation: the backtrace I get is this one:
> 
> [  124.956725] =================================
> [  124.957217] [ INFO: inconsistent lock state ]
> [  124.957217] 3.5.0+ #99 Not tainted
> [  124.957217] ---------------------------------
> [  124.957217] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
> [  124.957217] ksoftirqd/0/3 [HC0[0]:SC1[1]:HE1:SE0] takes:
> [  124.957217]  (&(&ss->id_lock)->rlock){+.?...}, at:
> [<ffffffff810aa7b2>] spin_lock+0x9/0xb
> [  124.957217] {SOFTIRQ-ON-W} state was registered at:
> [  124.957217]   [<ffffffff810996ed>] __lock_acquire+0x31f/0xd68
> [  124.957217]   [<ffffffff8109a660>] lock_acquire+0x108/0x15c
> [  124.957217]   [<ffffffff81534ec4>] _raw_spin_lock+0x40/0x4f
> [  124.957217]   [<ffffffff810aa7b2>] spin_lock+0x9/0xb
> [  124.957217]   [<ffffffff810ad00e>] get_new_cssid+0x69/0xf3
> [  124.957217]   [<ffffffff810ad0da>] cgroup_init_idr+0x42/0x60
> [  124.957217]   [<ffffffff81b20e04>] cgroup_init+0x50/0x100
> [  124.957217]   [<ffffffff81b05b9b>] start_kernel+0x3b9/0x3ee
> [  124.957217]   [<ffffffff81b052d6>] x86_64_start_reservations+0xb1/0xb5
> [  124.957217]   [<ffffffff81b053d8>] x86_64_start_kernel+0xfe/0x10b
> 
> 
> So what we learn from it, is: we are acquiring a specific lock (the css
> id one) from softirq context. It was previously taken in a
> softirq-enabled context, that seems to be coming directly from
> get_new_cssid.
> 
> Tejun correctly pointed out that we should never acquire that lock from
> a softirq context, in which he is right.
> 
> But the situation changes slightly with kmem. Now, the following excerpt
> of a backtrace is possible:
> 
> [   48.602775]  [<ffffffff81103095>] free_accounted_pages+0x47/0x4c
> [   48.602775]  [<ffffffff81047f90>] free_task+0x31/0x5c
> [   48.602775]  [<ffffffff8104807d>] __put_task_struct+0xc2/0xdb
> [   48.602775]  [<ffffffff8104dfc7>] put_task_struct+0x1e/0x22
> [   48.602775]  [<ffffffff8104e144>] delayed_put_task_struct+0x7a/0x98
> [   48.602775]  [<ffffffff810cf0e5>] __rcu_process_callbacks+0x269/0x3df
> [   48.602775]  [<ffffffff810cf28c>] rcu_process_callbacks+0x31/0x5b
> [   48.602775]  [<ffffffff8105266d>] __do_softirq+0x122/0x277
> 
> So as you can see, free_accounted_pages (that will trigger a memcg_put()
> -> mem_cgroup_free()) can now be called from softirq context, which is,
> an rcu callback (and I just realized I wrote the exact opposite in the
> subj line: man, I really suck at that!!)
> As a matter of fact, we could not move to our rcu callback as well:
> 
> we need to move it to a worker thread with the rest.
> 
> We already have a worker thread: he reason we have it is not
> static_branches: The reason is vfree(), that will BUG_ON(in_interrupt())
> and could not be called from rcu callback as well. We moved static
> branches in there as well for a similar problem, but haven't introduced it.
> 
> Could we move just part of it to the worker thread? Absolutely yes.
> Moving just free_css_id() is enough to make it work. But since it is not
> the first context related problem we had, I thought: "to hell with that,
> let's move everything and be safe".
> 
> I am fine moving free_css_id() only if you would prefer.
> 
> Can we disable softirqs when we initialize css_id? Maybe. My machine
> seems to boot fine and survive the simple workload that would trigger
> that bug if I use irqsave spinlocks instead of normal spinlocks. But
> this has to be done from cgroup core: We have no control over css
> creation in memcg.
> 
> How would you guys like me to handle this ?

One more thing: As I mentioned in the Changelog,
mem_cgroup_remove_exceeded(), called from mem_cgroup_remove_from_trees()
will lead to the same usage pattern.




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Re: [PATCH v3 12/13] execute the whole memcg freeing in rcu callback

[Johannes Weiner]

On Thu, Oct 04, 2012 at 02:53:13PM +0400, Glauber Costa wrote:
> On 10/01/2012 05:27 PM, Michal Hocko wrote:
> > On Tue 18-09-12 18:04:09, Glauber Costa wrote:
> >> A lot of the initialization we do in mem_cgroup_create() is done with softirqs
> >> enabled. This include grabbing a css id, which holds &ss->id_lock->rlock, and
> >> the per-zone trees, which holds rtpz->lock->rlock. All of those signal to the
> >> lockdep mechanism that those locks can be used in SOFTIRQ-ON-W context. This
> >> means that the freeing of memcg structure must happen in a compatible context,
> >> otherwise we'll get a deadlock.
> > 
> > Maybe I am missing something obvious but why cannot we simply disble
> > (soft)irqs in mem_cgroup_create rather than make the free path much more
> > complicated. It really feels strange to defer everything (e.g. soft
> > reclaim tree cleanup which should be a no-op at the time because there
> > shouldn't be any user pages in the group).
> > 
> 
> Ok.
> 
> I was just able to come back to this today - I was mostly working on the
> slab feedback over the past few days. I will answer yours and Tejun's
> concerns at once:
> 
> Here is the situation: the backtrace I get is this one:
> 
> [  124.956725] =================================
> [  124.957217] [ INFO: inconsistent lock state ]
> [  124.957217] 3.5.0+ #99 Not tainted
> [  124.957217] ---------------------------------
> [  124.957217] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
> [  124.957217] ksoftirqd/0/3 [HC0[0]:SC1[1]:HE1:SE0] takes:
> [  124.957217]  (&(&ss->id_lock)->rlock){+.?...}, at:
> [<ffffffff810aa7b2>] spin_lock+0x9/0xb
> [  124.957217] {SOFTIRQ-ON-W} state was registered at:
> [  124.957217]   [<ffffffff810996ed>] __lock_acquire+0x31f/0xd68
> [  124.957217]   [<ffffffff8109a660>] lock_acquire+0x108/0x15c
> [  124.957217]   [<ffffffff81534ec4>] _raw_spin_lock+0x40/0x4f
> [  124.957217]   [<ffffffff810aa7b2>] spin_lock+0x9/0xb
> [  124.957217]   [<ffffffff810ad00e>] get_new_cssid+0x69/0xf3
> [  124.957217]   [<ffffffff810ad0da>] cgroup_init_idr+0x42/0x60
> [  124.957217]   [<ffffffff81b20e04>] cgroup_init+0x50/0x100
> [  124.957217]   [<ffffffff81b05b9b>] start_kernel+0x3b9/0x3ee
> [  124.957217]   [<ffffffff81b052d6>] x86_64_start_reservations+0xb1/0xb5
> [  124.957217]   [<ffffffff81b053d8>] x86_64_start_kernel+0xfe/0x10b
> 
> 
> So what we learn from it, is: we are acquiring a specific lock (the css
> id one) from softirq context. It was previously taken in a
> softirq-enabled context, that seems to be coming directly from
> get_new_cssid.
> 
> Tejun correctly pointed out that we should never acquire that lock from
> a softirq context, in which he is right.
> 
> But the situation changes slightly with kmem. Now, the following excerpt
> of a backtrace is possible:
> 
> [   48.602775]  [<ffffffff81103095>] free_accounted_pages+0x47/0x4c
> [   48.602775]  [<ffffffff81047f90>] free_task+0x31/0x5c
> [   48.602775]  [<ffffffff8104807d>] __put_task_struct+0xc2/0xdb
> [   48.602775]  [<ffffffff8104dfc7>] put_task_struct+0x1e/0x22
> [   48.602775]  [<ffffffff8104e144>] delayed_put_task_struct+0x7a/0x98
> [   48.602775]  [<ffffffff810cf0e5>] __rcu_process_callbacks+0x269/0x3df
> [   48.602775]  [<ffffffff810cf28c>] rcu_process_callbacks+0x31/0x5b
> [   48.602775]  [<ffffffff8105266d>] __do_softirq+0x122/0x277
> 
> So as you can see, free_accounted_pages (that will trigger a memcg_put()
> -> mem_cgroup_free()) can now be called from softirq context, which is,
> an rcu callback (and I just realized I wrote the exact opposite in the
> subj line: man, I really suck at that!!)
> As a matter of fact, we could not move to our rcu callback as well:
> 
> we need to move it to a worker thread with the rest.
> 
> We already have a worker thread: he reason we have it is not
> static_branches: The reason is vfree(), that will BUG_ON(in_interrupt())
> and could not be called from rcu callback as well. We moved static
> branches in there as well for a similar problem, but haven't introduced it.
> 
> Could we move just part of it to the worker thread? Absolutely yes.
> Moving just free_css_id() is enough to make it work. But since it is not
> the first context related problem we had, I thought: "to hell with that,
> let's move everything and be safe".
> 
> I am fine moving free_css_id() only if you would prefer.
> 
> Can we disable softirqs when we initialize css_id? Maybe. My machine
> seems to boot fine and survive the simple workload that would trigger
> that bug if I use irqsave spinlocks instead of normal spinlocks. But
> this has to be done from cgroup core: We have no control over css
> creation in memcg.
> 
> How would you guys like me to handle this ?

Without the vfree callback, I would have preferred just making the
id_lock softirq safe.  But since we have to defer (parts of) freeing
anyway, I like your approach of just deferring the rest as well
better.

But please add comments why the stuff in there is actually deferred.
Just simple notes like:

"this can be called from atomic contexts, <examples>",

"vfree must run from process context" and "css_id locking is not soft
irq safe",

"to hell with that, let's just do everything from the workqueue and be
safe and simple".

(And this may be personal preference, but why have free_work call
__mem_cgroup_free()?  Does anyone else need to call that code?  There
are too many layers already, why not just keep it all in free_work()
and have one less stack frame on your mind? :))

As for the changelog, here is my attempt:

---

mm: memcg: defer whole memcg tear-down to workqueue

The final memcg put can already happen in atomic context and so the
freeing is deferred to a workqueue because it needs to use vfree().

Kmem tracking will add freeing from softirq context, but the id_lock
acquired when destroying the cgroup object is not softirq safe, e.g.:

> [   48.602775]  [<ffffffff81103095>] free_accounted_pages+0x47/0x4c
> [   48.602775]  [<ffffffff81047f90>] free_task+0x31/0x5c
> [   48.602775]  [<ffffffff8104807d>] __put_task_struct+0xc2/0xdb
> [   48.602775]  [<ffffffff8104dfc7>] put_task_struct+0x1e/0x22
> [   48.602775]  [<ffffffff8104e144>] delayed_put_task_struct+0x7a/0x98
> [   48.602775]  [<ffffffff810cf0e5>] __rcu_process_callbacks+0x269/0x3df
> [   48.602775]  [<ffffffff810cf28c>] rcu_process_callbacks+0x31/0x5b
> [   48.602775]  [<ffffffff8105266d>] __do_softirq+0x122/0x277

To avoid making tear-down too complicated - making locks soft irq
safe, having half the cleanup in one function on the other half
somewhere else - just defer everything to the workqueue.

Re: [PATCH v3 12/13] execute the whole memcg freeing in rcu callback

[Glauber Costa]

On 10/05/2012 07:31 PM, Johannes Weiner wrote:
> On Thu, Oct 04, 2012 at 02:53:13PM +0400, Glauber Costa wrote:
>> On 10/01/2012 05:27 PM, Michal Hocko wrote:
>>> On Tue 18-09-12 18:04:09, Glauber Costa wrote:
>>>> A lot of the initialization we do in mem_cgroup_create() is done with softirqs
>>>> enabled. This include grabbing a css id, which holds &ss->id_lock->rlock, and
>>>> the per-zone trees, which holds rtpz->lock->rlock. All of those signal to the
>>>> lockdep mechanism that those locks can be used in SOFTIRQ-ON-W context. This
>>>> means that the freeing of memcg structure must happen in a compatible context,
>>>> otherwise we'll get a deadlock.
>>>
>>> Maybe I am missing something obvious but why cannot we simply disble
>>> (soft)irqs in mem_cgroup_create rather than make the free path much more
>>> complicated. It really feels strange to defer everything (e.g. soft
>>> reclaim tree cleanup which should be a no-op at the time because there
>>> shouldn't be any user pages in the group).
>>>
>>
>> Ok.
>>
>> I was just able to come back to this today - I was mostly working on the
>> slab feedback over the past few days. I will answer yours and Tejun's
>> concerns at once:
>>
>> Here is the situation: the backtrace I get is this one:
>>
>> [  124.956725] =================================
>> [  124.957217] [ INFO: inconsistent lock state ]
>> [  124.957217] 3.5.0+ #99 Not tainted
>> [  124.957217] ---------------------------------
>> [  124.957217] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
>> [  124.957217] ksoftirqd/0/3 [HC0[0]:SC1[1]:HE1:SE0] takes:
>> [  124.957217]  (&(&ss->id_lock)->rlock){+.?...}, at:
>> [<ffffffff810aa7b2>] spin_lock+0x9/0xb
>> [  124.957217] {SOFTIRQ-ON-W} state was registered at:
>> [  124.957217]   [<ffffffff810996ed>] __lock_acquire+0x31f/0xd68
>> [  124.957217]   [<ffffffff8109a660>] lock_acquire+0x108/0x15c
>> [  124.957217]   [<ffffffff81534ec4>] _raw_spin_lock+0x40/0x4f
>> [  124.957217]   [<ffffffff810aa7b2>] spin_lock+0x9/0xb
>> [  124.957217]   [<ffffffff810ad00e>] get_new_cssid+0x69/0xf3
>> [  124.957217]   [<ffffffff810ad0da>] cgroup_init_idr+0x42/0x60
>> [  124.957217]   [<ffffffff81b20e04>] cgroup_init+0x50/0x100
>> [  124.957217]   [<ffffffff81b05b9b>] start_kernel+0x3b9/0x3ee
>> [  124.957217]   [<ffffffff81b052d6>] x86_64_start_reservations+0xb1/0xb5
>> [  124.957217]   [<ffffffff81b053d8>] x86_64_start_kernel+0xfe/0x10b
>>
>>
>> So what we learn from it, is: we are acquiring a specific lock (the css
>> id one) from softirq context. It was previously taken in a
>> softirq-enabled context, that seems to be coming directly from
>> get_new_cssid.
>>
>> Tejun correctly pointed out that we should never acquire that lock from
>> a softirq context, in which he is right.
>>
>> But the situation changes slightly with kmem. Now, the following excerpt
>> of a backtrace is possible:
>>
>> [   48.602775]  [<ffffffff81103095>] free_accounted_pages+0x47/0x4c
>> [   48.602775]  [<ffffffff81047f90>] free_task+0x31/0x5c
>> [   48.602775]  [<ffffffff8104807d>] __put_task_struct+0xc2/0xdb
>> [   48.602775]  [<ffffffff8104dfc7>] put_task_struct+0x1e/0x22
>> [   48.602775]  [<ffffffff8104e144>] delayed_put_task_struct+0x7a/0x98
>> [   48.602775]  [<ffffffff810cf0e5>] __rcu_process_callbacks+0x269/0x3df
>> [   48.602775]  [<ffffffff810cf28c>] rcu_process_callbacks+0x31/0x5b
>> [   48.602775]  [<ffffffff8105266d>] __do_softirq+0x122/0x277
>>
>> So as you can see, free_accounted_pages (that will trigger a memcg_put()
>> -> mem_cgroup_free()) can now be called from softirq context, which is,
>> an rcu callback (and I just realized I wrote the exact opposite in the
>> subj line: man, I really suck at that!!)
>> As a matter of fact, we could not move to our rcu callback as well:
>>
>> we need to move it to a worker thread with the rest.
>>
>> We already have a worker thread: he reason we have it is not
>> static_branches: The reason is vfree(), that will BUG_ON(in_interrupt())
>> and could not be called from rcu callback as well. We moved static
>> branches in there as well for a similar problem, but haven't introduced it.
>>
>> Could we move just part of it to the worker thread? Absolutely yes.
>> Moving just free_css_id() is enough to make it work. But since it is not
>> the first context related problem we had, I thought: "to hell with that,
>> let's move everything and be safe".
>>
>> I am fine moving free_css_id() only if you would prefer.
>>
>> Can we disable softirqs when we initialize css_id? Maybe. My machine
>> seems to boot fine and survive the simple workload that would trigger
>> that bug if I use irqsave spinlocks instead of normal spinlocks. But
>> this has to be done from cgroup core: We have no control over css
>> creation in memcg.
>>
>> How would you guys like me to handle this ?
> 
> Without the vfree callback, I would have preferred just making the
> id_lock softirq safe.  But since we have to defer (parts of) freeing
> anyway, I like your approach of just deferring the rest as well
> better.
> 
> But please add comments why the stuff in there is actually deferred.
> Just simple notes like:
> 
> "this can be called from atomic contexts, <examples>",
> 
> "vfree must run from process context" and "css_id locking is not soft
> irq safe",
> 
> "to hell with that, let's just do everything from the workqueue and be
> safe and simple".
> 
> (And this may be personal preference, but why have free_work call
> __mem_cgroup_free()?  Does anyone else need to call that code?  There
> are too many layers already, why not just keep it all in free_work()
> and have one less stack frame on your mind? :))
> 
It is used when create fails.

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[PATCH v3 13/13] protect architectures where THREAD_SIZE >= PAGE_SIZE against fork bombs

[Glauber Costa]

Because those architectures will draw their stacks directly from the
page allocator, rather than the slab cache, we can directly pass
__GFP_KMEMCG flag, and issue the corresponding free_pages.

This code path is taken when the architecture doesn't define
CONFIG_ARCH_THREAD_INFO_ALLOCATOR (only ia64 seems to), and has
THREAD_SIZE >= PAGE_SIZE. Luckily, most - if not all - of the remaining
architectures fall in this category.

This will guarantee that every stack page is accounted to the memcg the
process currently lives on, and will have the allocations to fail if
they go over limit.

For the time being, I am defining a new variant of THREADINFO_GFP, not
to mess with the other path. Once the slab is also tracked by memcg, we
can get rid of that flag.

Tested to successfully protect against :(){ :|:& };:

Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
Acked-by: Frederic Weisbecker <fweisbec-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
CC: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
CC: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
---
 include/linux/thread_info.h | 2 ++
 kernel/fork.c               | 4 ++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index ccc1899..e7e0473 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -61,6 +61,8 @@ extern long do_no_restart_syscall(struct restart_block *parm);
 # define THREADINFO_GFP		(GFP_KERNEL | __GFP_NOTRACK)
 #endif
 
+#define THREADINFO_GFP_ACCOUNTED (THREADINFO_GFP | __GFP_KMEMCG)
+
 /*
  * flag set/clear/test wrappers
  * - pass TIF_xxxx constants to these functions
diff --git a/kernel/fork.c b/kernel/fork.c
index 0ff2bf7..897e89c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -146,7 +146,7 @@ void __weak arch_release_thread_info(struct thread_info *ti)
 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 						  int node)
 {
-	struct page *page = alloc_pages_node(node, THREADINFO_GFP,
+	struct page *page = alloc_pages_node(node, THREADINFO_GFP_ACCOUNTED,
 					     THREAD_SIZE_ORDER);
 
 	return page ? page_address(page) : NULL;
@@ -154,7 +154,7 @@ static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 
 static inline void free_thread_info(struct thread_info *ti)
 {
-	free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
+	free_accounted_pages((unsigned long)ti, THREAD_SIZE_ORDER);
 }
 # else
 static struct kmem_cache *thread_info_cache;
-- 
1.7.11.4

Re: [PATCH v3 13/13] protect architectures where THREAD_SIZE >= PAGE_SIZE against fork bombs

[Michal Hocko]

On Tue 18-09-12 18:04:10, Glauber Costa wrote:
> Because those architectures will draw their stacks directly from the
> page allocator, rather than the slab cache, we can directly pass
> __GFP_KMEMCG flag, and issue the corresponding free_pages.
> 
> This code path is taken when the architecture doesn't define
> CONFIG_ARCH_THREAD_INFO_ALLOCATOR (only ia64 seems to), and has
> THREAD_SIZE >= PAGE_SIZE. Luckily, most - if not all - of the remaining
> architectures fall in this category.
> 
> This will guarantee that every stack page is accounted to the memcg the
> process currently lives on, and will have the allocations to fail if
> they go over limit.
> 
> For the time being, I am defining a new variant of THREADINFO_GFP, not
> to mess with the other path. Once the slab is also tracked by memcg, we
> can get rid of that flag.
> 
> Tested to successfully protect against :(){ :|:& };:

OK. Although I was complaining that this is not the full truth the last
time, I do not insist on gravy details about the slaughter this will
cause to the rest of the group and that who-ever could fork in the group
can easily DOS the whole hierarchy. It has some interesting side effects
as well but let's keep this to a careful reader ;)

The patch, as is, is still useful and an improvement because it reduces
the impact.

> 
> Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
> Acked-by: Frederic Weisbecker <fweisbec-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
> CC: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>
> CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
> CC: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
> CC: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> CC: Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>

Reviewed-by: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>

> ---
>  include/linux/thread_info.h | 2 ++
>  kernel/fork.c               | 4 ++--
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
> index ccc1899..e7e0473 100644
> --- a/include/linux/thread_info.h
> +++ b/include/linux/thread_info.h
> @@ -61,6 +61,8 @@ extern long do_no_restart_syscall(struct restart_block *parm);
>  # define THREADINFO_GFP		(GFP_KERNEL | __GFP_NOTRACK)
>  #endif
>  
> +#define THREADINFO_GFP_ACCOUNTED (THREADINFO_GFP | __GFP_KMEMCG)
> +
>  /*
>   * flag set/clear/test wrappers
>   * - pass TIF_xxxx constants to these functions
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 0ff2bf7..897e89c 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -146,7 +146,7 @@ void __weak arch_release_thread_info(struct thread_info *ti)
>  static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
>  						  int node)
>  {
> -	struct page *page = alloc_pages_node(node, THREADINFO_GFP,
> +	struct page *page = alloc_pages_node(node, THREADINFO_GFP_ACCOUNTED,
>  					     THREAD_SIZE_ORDER);
>  
>  	return page ? page_address(page) : NULL;
> @@ -154,7 +154,7 @@ static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
>  
>  static inline void free_thread_info(struct thread_info *ti)
>  {
> -	free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
> +	free_accounted_pages((unsigned long)ti, THREAD_SIZE_ORDER);
>  }
>  # else
>  static struct kmem_cache *thread_info_cache;
> -- 
> 1.7.11.4
> 
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Michal Hocko
SUSE Labs