[patch 08/12] mm: memcontrol: use root_mem_cgroup res_counter

Johannes Weiner
2014-06-16T19:54:28Z

Due to an old optimization to keep expensive res_counter changes at a
minimum, the root_mem_cgroup res_counter is never charged; there is no
limit at that level anyway, and any statistics can be generated on
demand by summing up the counters of all other cgroups.

However, with per-cpu charge caches, res_counter operations do not
even show up in profiles anymore, so this optimization is no longer
necessary.

Remove it to simplify the code.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
---
mm/memcontrol.c | 150 ++++++++++++++++----------------------------------------
1 file changed, 43 insertions(+), 107 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a3b69d4a6f17..3726f6774860 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2572,9 +2572,8 @@ static int mem_cgroup_try_charge(struct mem_cgroup *memcg,
unsigned long nr_reclaimed;
unsigned long flags = 0;
unsigned long long size;
+ int ret = 0;

- if (mem_cgroup_is_root(memcg))
- goto done;
retry:
if (consume_stock(memcg, nr_pages))
goto done;
@@ -2655,13 +2654,15 @@ nomem:
if (!(gfp_mask & __GFP_NOFAIL))
return -ENOMEM;
bypass:
- return -EINTR;
+ memcg = root_mem_cgroup;
+ ret = -EINTR;
+ goto retry;

done_restock:
if (batch > nr_pages)
refill_stock(memcg, batch - nr_pages);
done:
- return 0;
+ return ret;
}

/**
@@ -2701,13 +2702,11 @@ static struct mem_cgroup *mem_cgroup_try_charge_mm(struct mm_struct *mm,
static void __mem_cgroup_cancel_charge(struct mem_cgroup *memcg,
unsigned int nr_pages)
{
- if (!mem_cgroup_is_root(memcg)) {
- unsigned long bytes = nr_pages * PAGE_SIZE;
+ unsigned long bytes = nr_pages * PAGE_SIZE;

- res_counter_uncharge(&memcg->res, bytes);
- if (do_swap_account)
- res_counter_uncharge(&memcg->memsw, bytes);
- }
+ res_counter_uncharge(&memcg->res, bytes);
+ if (do_swap_account)
+ res_counter_uncharge(&memcg->memsw, bytes);
}

/*
@@ -2719,9 +2718,6 @@ static void __mem_cgroup_cancel_local_charge(struct mem_cgroup *memcg,
{
unsigned long bytes = nr_pages * PAGE_SIZE;

- if (mem_cgroup_is_root(memcg))
- return;
-
res_counter_uncharge_until(&memcg->res, memcg->res.parent, bytes);
if (do_swap_account)
res_counter_uncharge_until(&memcg->memsw,
@@ -3956,7 +3952,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype,
* replacement page, so leave it alone when phasing out the
* page that is unused after the migration.
*/
- if (!end_migration && !mem_cgroup_is_root(memcg))
+ if (!end_migration)
mem_cgroup_do_uncharge(memcg, nr_pages, ctype);

return memcg;
@@ -4089,8 +4085,7 @@ void mem_cgroup_uncharge_swap(swp_entry_t ent)
* We uncharge this because swap is freed. This memcg can
* be obsolete one. We avoid calling css_tryget_online().
*/
- if (!mem_cgroup_is_root(memcg))
- res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
+ res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
mem_cgroup_swap_statistics(memcg, false);
css_put(&memcg->css);
}
@@ -4780,78 +4775,24 @@ out:
return retval;
}

-
-static unsigned long mem_cgroup_recursive_stat(struct mem_cgroup *memcg,
- enum mem_cgroup_stat_index idx)
-{
- struct mem_cgroup *iter;
- long val = 0;
-
- /* Per-cpu values can be negative, use a signed accumulator */
- for_each_mem_cgroup_tree(iter, memcg)
- val += mem_cgroup_read_stat(iter, idx);
-
- if (val < 0) /* race ? */
- val = 0;
- return val;
-}
-
-static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
-{
- u64 val;
-
- if (!mem_cgroup_is_root(memcg)) {
- if (!swap)
- return res_counter_read_u64(&memcg->res, RES_USAGE);
- else
- return res_counter_read_u64(&memcg->memsw, RES_USAGE);
- }
-
- /*
- * Transparent hugepages are still accounted for in MEM_CGROUP_STAT_RSS
- * as well as in MEM_CGROUP_STAT_RSS_HUGE.
- */
- val = mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_CACHE);
- val += mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_RSS);
-
- if (swap)
- val += mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_SWAP);
-
- return val << PAGE_SHIFT;
-}
-
static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css,
- struct cftype *cft)
+ struct cftype *cft)
{
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
- u64 val;
- int name;
- enum res_type type;
-
- type = MEMFILE_TYPE(cft->private);
- name = MEMFILE_ATTR(cft->private);
+ enum res_type type = MEMFILE_TYPE(cft->private);
+ int name = MEMFILE_ATTR(cft->private);

switch (type) {
case _MEM:
- if (name == RES_USAGE)
- val = mem_cgroup_usage(memcg, false);
- else
- val = res_counter_read_u64(&memcg->res, name);
- break;
+ return res_counter_read_u64(&memcg->res, name);
case _MEMSWAP:
- if (name == RES_USAGE)
- val = mem_cgroup_usage(memcg, true);
- else
- val = res_counter_read_u64(&memcg->memsw, name);
- break;
+ return res_counter_read_u64(&memcg->memsw, name);
case _KMEM:
- val = res_counter_read_u64(&memcg->kmem, name);
+ return res_counter_read_u64(&memcg->kmem, name);
break;
default:
BUG();
}
-
- return val;
}

#ifdef CONFIG_MEMCG_KMEM
@@ -5313,7 +5254,10 @@ static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
if (!t)
goto unlock;

- usage = mem_cgroup_usage(memcg, swap);
+ if (!swap)
+ usage = res_counter_read_u64(&memcg->res, RES_USAGE);
+ else
+ usage = res_counter_read_u64(&memcg->memsw, RES_USAGE);

/*
* current_threshold points to threshold just below or equal to usage.
@@ -5405,15 +5349,15 @@ static int __mem_cgroup_usage_register_event(struct mem_cgroup *memcg,

mutex_lock(&memcg->thresholds_lock);

- if (type == _MEM)
+ if (type == _MEM) {
thresholds = &memcg->thresholds;
- else if (type == _MEMSWAP)
+ usage = res_counter_read_u64(&memcg->res, RES_USAGE);
+ } else if (type == _MEMSWAP) {
thresholds = &memcg->memsw_thresholds;
- else
+ usage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
+ } else
BUG();

- usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
-
/* Check if a threshold crossed before adding a new one */
if (thresholds->primary)
__mem_cgroup_threshold(memcg, type == _MEMSWAP);
@@ -5493,18 +5437,19 @@ static void __mem_cgroup_usage_unregister_event(struct mem_cgroup *memcg,
int i, j, size;

mutex_lock(&memcg->thresholds_lock);
- if (type == _MEM)
+
+ if (type == _MEM) {
thresholds = &memcg->thresholds;
- else if (type == _MEMSWAP)
+ usage = res_counter_read_u64(&memcg->res, RES_USAGE);
+ } else if (type == _MEMSWAP) {
thresholds = &memcg->memsw_thresholds;
- else
+ usage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
+ } else
BUG();

if (!thresholds->primary)
goto unlock;

- usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
-
/* Check if a threshold crossed before removing */
__mem_cgroup_threshold(memcg, type == _MEMSWAP);

@@ -6259,9 +6204,9 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
* core guarantees its existence.
*/
} else {
- res_counter_init(&memcg->res, NULL);
- res_counter_init(&memcg->memsw, NULL);
- res_counter_init(&memcg->kmem, NULL);
+ res_counter_init(&memcg->res, &root_mem_cgroup->res);
+ res_counter_init(&memcg->memsw, &root_mem_cgroup->memsw);
+ res_counter_init(&memcg->kmem, &root_mem_cgroup->kmem);
/*
* Deeper hierachy with use_hierarchy == false doesn't make
* much sense so let cgroup subsystem know about this
@@ -6376,12 +6321,6 @@ static int mem_cgroup_do_precharge(unsigned long count)
{
int ret;

- if (mem_cgroup_is_root(mc.to)) {
- mc.precharge += count;
- /* we don't need css_get for root */
- return ret;
- }
-
/* Try a single bulk charge without reclaim first */
ret = mem_cgroup_try_charge(mc.to, GFP_KERNEL & ~__GFP_WAIT,
count, false);
@@ -6687,21 +6626,18 @@ static void __mem_cgroup_clear_mc(void)
/* we must fixup refcnts and charges */
if (mc.moved_swap) {
/* uncharge swap account from the old cgroup */
- if (!mem_cgroup_is_root(mc.from))
- res_counter_uncharge(&mc.from->memsw,
- PAGE_SIZE * mc.moved_swap);
+ res_counter_uncharge(&mc.from->memsw,
+ PAGE_SIZE * mc.moved_swap);

for (i = 0; i < mc.moved_swap; i++)
css_put(&mc.from->css);

- if (!mem_cgroup_is_root(mc.to)) {
- /*
- * we charged both to->res and to->memsw, so we should
- * uncharge to->res.
- */
- res_counter_uncharge(&mc.to->res,
- PAGE_SIZE * mc.moved_swap);
- }
+ /*
+ * we charged both to->res and to->memsw, so we should
+ * uncharge to->res.
+ */
+ res_counter_uncharge(&mc.to->res,
+ PAGE_SIZE * mc.moved_swap);
/* we've already done css_get(mc.to) */
mc.moved_swap = 0;
}
--
2.0.0