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mm: memcontrol: do not acquire page_cgroup lock for kmem pages 

Kmem page charging and uncharging is serialized by means of exclusive
access to the page.  Do not take the page_cgroup lock and don't set
pc->flags atomically.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2014-08-06 16:06:04 -07:00 committed by Linus Torvalds
parent 9a2385eef9
commit a840cda63e
1 changed files with 7 additions and 14 deletions
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21
mm/memcontrol.c
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@ -3407,12 +3407,13 @@ void __memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg,
memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
return;
}
/*
* The page is freshly allocated and not visible to any
* outside callers yet. Set up pc non-atomically.
*/
pc = lookup_page_cgroup(page);
lock_page_cgroup(pc);
pc->mem_cgroup = memcg;
SetPageCgroupUsed(pc);
unlock_page_cgroup(pc);
pc->flags = PCG_USED;
}
void __memcg_kmem_uncharge_pages(struct page *page, int order)
@ -3422,19 +3423,11 @@ void __memcg_kmem_uncharge_pages(struct page *page, int order)
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);
memcg = pc->mem_cgroup;
pc->flags = 0;
/*
* We trust that only if there is a memcg associated with the page, it