[PATCHSET] mm, memcontrol: Implement memory.swap.events

[PATCHSET] mm, memcontrol: Implement memory.swap.events

[Tejun Heo]

Hello,

This patchset implements memory.swap.events which contains max and
fail events so that userland can monitor and respond to swap running
out.  It contains the following two patches.

 0001-mm-memcontrol-Move-swap-charge-handling-into-get_swa.patch
 0002-mm-memcontrol-Implement-memory.swap.events.patch

This patchset is on top of the "cgroup/for-4.17: Make cgroup_rstat
available to controllers" patchset[1] and "mm, memcontrol: Make
cgroup_rstat available to controllers" patchset[2] and also available
in the following git branch.

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-memcg-swap.events

diffstat follows.

 Documentation/cgroup-v2.txt |   16 ++++++++++++++++
 include/linux/memcontrol.h  |    5 +++++
 mm/memcontrol.c             |   25 +++++++++++++++++++++++++
 mm/shmem.c                  |    4 ----
 mm/swap_slots.c             |   10 +++++++---
 mm/swap_state.c             |    3 ---
 6 files changed, 53 insertions(+), 10 deletions(-)

Thanks.

--
tejun

[1] http://lkml.kernel.org/r/20180323231313.1254142-1-tj@kernel.org
[2] http://lkml.kernel.org/r/20180324160901.512135-1-tj@kernel.org

[PATCH 1/2] mm, memcontrol: Move swap charge handling into get_swap_page()

[Tejun Heo]

get_swap_page() is always followed by mem_cgroup_try_charge_swap().
This patch moves mem_cgroup_try_charge_swap() into get_swap_page() and
makes get_swap_page() call the function even after swap allocation
failure.

This simplifies the callers and consolidates memcg related logic and
will ease adding swap related memcg events.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 mm/memcontrol.c |  3 +++
 mm/shmem.c      |  4 ----
 mm/swap_slots.c | 10 +++++++---
 mm/swap_state.c |  3 ---
 4 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d5bf01d..9f9c8a7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5987,6 +5987,9 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
 	if (!memcg)
 		return 0;
 
+	if (!entry.val)
+		return 0;
+
 	memcg = mem_cgroup_id_get_online(memcg);
 
 	if (!mem_cgroup_is_root(memcg) &&
diff --git a/mm/shmem.c b/mm/shmem.c
index 1907688..4a07d21 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1313,9 +1313,6 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 	if (!swap.val)
 		goto redirty;
 
-	if (mem_cgroup_try_charge_swap(page, swap))
-		goto free_swap;
-
 	/*
 	 * Add inode to shmem_unuse()'s list of swapped-out inodes,
 	 * if it's not already there.  Do it now before the page is
@@ -1344,7 +1341,6 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 	}
 
 	mutex_unlock(&shmem_swaplist_mutex);
-free_swap:
 	put_swap_page(page, swap);
 redirty:
 	set_page_dirty(page);
diff --git a/mm/swap_slots.c b/mm/swap_slots.c
index bebc192..7546eb2 100644
--- a/mm/swap_slots.c
+++ b/mm/swap_slots.c
@@ -319,7 +319,7 @@ swp_entry_t get_swap_page(struct page *page)
 	if (PageTransHuge(page)) {
 		if (IS_ENABLED(CONFIG_THP_SWAP))
 			get_swap_pages(1, true, &entry);
-		return entry;
+		goto out;
 	}
 
 	/*
@@ -349,11 +349,15 @@ swp_entry_t get_swap_page(struct page *page)
 		}
 		mutex_unlock(&cache->alloc_lock);
 		if (entry.val)
-			return entry;
+			goto out;
 	}
 
 	get_swap_pages(1, false, &entry);
-
+out:
+	if (mem_cgroup_try_charge_swap(page, entry)) {
+		put_swap_page(page, entry);
+		entry.val = 0;
+	}
 	return entry;
 }
 
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 39ae7cf..41f0809 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -216,9 +216,6 @@ int add_to_swap(struct page *page)
 	if (!entry.val)
 		return 0;
 
-	if (mem_cgroup_try_charge_swap(page, entry))
-		goto fail;
-
 	/*
 	 * Radix-tree node allocations from PF_MEMALLOC contexts could
 	 * completely exhaust the page allocator. __GFP_NOMEMALLOC
-- 
2.9.5

[PATCH 2/2] mm, memcontrol: Implement memory.swap.events

[Tejun Heo]

Add swap max and fail events so that userland can monitor and respond
to running out of swap.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-api@vger.kernel.org
---
 Documentation/cgroup-v2.txt | 16 ++++++++++++++++
 include/linux/memcontrol.h  |  5 +++++
 mm/memcontrol.c             | 24 +++++++++++++++++++++++-
 3 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index 74cdeae..b0dda10 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -1199,6 +1199,22 @@ PAGE_SIZE multiple when read back.
 	Swap usage hard limit.  If a cgroup's swap usage reaches this
 	limit, anonymous memory of the cgroup will not be swapped out.
 
+  memory.swap.events
+	A read-only flat-keyed file which exists on non-root cgroups.
+	The following entries are defined.  Unless specified
+	otherwise, a value change in this file generates a file
+	modified event.
+
+	  max
+		The number of times the cgroup's swap usage was about
+		to go over the max boundary and swap allocation
+		failed.
+
+	  fail
+		The number of times swap allocation failed either
+		because of running out of swap system-wide or max
+		limit.
+
 
 Usage Guidelines
 ~~~~~~~~~~~~~~~~
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 85a8f00..f198339 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -54,6 +54,8 @@ enum memcg_event_item {
 	MEMCG_HIGH,
 	MEMCG_MAX,
 	MEMCG_OOM,
+	MEMCG_SWAP_MAX,
+	MEMCG_SWAP_FAIL,
 	MEMCG_NR_EVENTS,
 };
 
@@ -202,6 +204,9 @@ struct mem_cgroup {
 	/* handle for "memory.events" */
 	struct cgroup_file events_file;
 
+	/* handle for "memory.swap.events" */
+	struct cgroup_file swap_events_file;
+
 	/* protect arrays of thresholds */
 	struct mutex thresholds_lock;
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9f9c8a7..1a14d4a4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5987,13 +5987,17 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
 	if (!memcg)
 		return 0;
 
-	if (!entry.val)
+	if (!entry.val) {
+		mem_cgroup_event(memcg, MEMCG_SWAP_FAIL);
 		return 0;
+	}
 
 	memcg = mem_cgroup_id_get_online(memcg);
 
 	if (!mem_cgroup_is_root(memcg) &&
 	    !page_counter_try_charge(&memcg->swap, nr_pages, &counter)) {
+		mem_cgroup_event(memcg, MEMCG_SWAP_MAX);
+		mem_cgroup_event(memcg, MEMCG_SWAP_FAIL);
 		mem_cgroup_id_put(memcg);
 		return -ENOMEM;
 	}
@@ -6131,6 +6135,18 @@ static ssize_t swap_max_write(struct kernfs_open_file *of,
 	return nbytes;
 }
 
+static int swap_events_show(struct seq_file *m, void *v)
+{
+	struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
+
+	memcg_stat_flush(memcg);
+
+	seq_printf(m, "max %llu\n", memcg->events[MEMCG_SWAP_MAX]);
+	seq_printf(m, "fail %llu\n", memcg->events[MEMCG_SWAP_FAIL]);
+
+	return 0;
+}
+
 static struct cftype swap_files[] = {
 	{
 		.name = "swap.current",
@@ -6143,6 +6159,12 @@ static struct cftype swap_files[] = {
 		.seq_show = swap_max_show,
 		.write = swap_max_write,
 	},
+	{
+		.name = "swap.events",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.file_offset = offsetof(struct mem_cgroup, swap_events_file),
+		.seq_show = swap_events_show,
+	},
 	{ }	/* terminate */
 };
 
-- 
2.9.5

Re: [PATCHSET] mm, memcontrol: Implement memory.swap.events

[Andrew Morton]

On Sat, 24 Mar 2018 09:51:25 -0700 Tejun Heo <tj@kernel.org> wrote:

> This patchset implements memory.swap.events which contains max and
> fail events so that userland can monitor and respond to swap running
> out.  It contains the following two patches.
> 
>  0001-mm-memcontrol-Move-swap-charge-handling-into-get_swa.patch
>  0002-mm-memcontrol-Implement-memory.swap.events.patch
> 
> This patchset is on top of the "cgroup/for-4.17: Make cgroup_rstat
> available to controllers" patchset[1] and "mm, memcontrol: Make
> cgroup_rstat available to controllers" patchset[2] and also available
> in the following git branch.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-memcg-swap.events

This doesn't appear to be in linux-next yet.  It should be by now if it's
targeted at 4.17?

Re: [PATCHSET] mm, memcontrol: Implement memory.swap.events

[Tejun Heo]

On Mon, Mar 26, 2018 at 02:39:31PM -0700, Andrew Morton wrote:
> On Sat, 24 Mar 2018 09:51:25 -0700 Tejun Heo <tj@kernel.org> wrote:
> 
> > This patchset implements memory.swap.events which contains max and
> > fail events so that userland can monitor and respond to swap running
> > out.  It contains the following two patches.
> > 
> >  0001-mm-memcontrol-Move-swap-charge-handling-into-get_swa.patch
> >  0002-mm-memcontrol-Implement-memory.swap.events.patch
> > 
> > This patchset is on top of the "cgroup/for-4.17: Make cgroup_rstat
> > available to controllers" patchset[1] and "mm, memcontrol: Make
> > cgroup_rstat available to controllers" patchset[2] and also available
> > in the following git branch.
> > 
> >  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-memcg-swap.events
> 
> This doesn't appear to be in linux-next yet.  It should be by now if it's
> targeted at 4.17?

You're right.  It's too late for 4.17.  Let's aim for 4.18.

Thanks.

-- 
tejun

Re: [PATCHSET] mm, memcontrol: Implement memory.swap.events

[Michal Hocko]

Hi Tejun,
sorry for the late response. Are you plannig to repost?

On Sat 24-03-18 09:51:25, Tejun Heo wrote:
> Hello,
> 
> This patchset implements memory.swap.events which contains max and
> fail events so that userland can monitor and respond to swap running
> out.  It contains the following two patches.
> 
>  0001-mm-memcontrol-Move-swap-charge-handling-into-get_swa.patch
>  0002-mm-memcontrol-Implement-memory.swap.events.patch
> 
> This patchset is on top of the "cgroup/for-4.17: Make cgroup_rstat
> available to controllers" patchset[1] and "mm, memcontrol: Make
> cgroup_rstat available to controllers" patchset[2] and also available
> in the following git branch.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-memcg-swap.events
> 
> diffstat follows.
> 
>  Documentation/cgroup-v2.txt |   16 ++++++++++++++++
>  include/linux/memcontrol.h  |    5 +++++
>  mm/memcontrol.c             |   25 +++++++++++++++++++++++++
>  mm/shmem.c                  |    4 ----
>  mm/swap_slots.c             |   10 +++++++---
>  mm/swap_state.c             |    3 ---
>  6 files changed, 53 insertions(+), 10 deletions(-)
> 
> Thanks.
> 
> --
> tejun
> 
> [1] http://lkml.kernel.org/r/20180323231313.1254142-1-tj@kernel.org
> [2] http://lkml.kernel.org/r/20180324160901.512135-1-tj@kernel.org

-- 
Michal Hocko
SUSE Labs

Re: [PATCHSET] mm, memcontrol: Implement memory.swap.events

[Tejun Heo]

On Thu, Apr 12, 2018 at 04:13:45PM +0200, Michal Hocko wrote:
> Hi Tejun,
> sorry for the late response. Are you plannig to repost?

Yeah, will do later.

Thanks.

-- 
tejun