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Commit a840cda6 authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
Browse files

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: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
Acked-by: default avatarVladimir Davydov <vdavydov@parallels.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 9a2385ee

mm/memcontrol.c

+7 −14
Original line number Diff line number Diff line
@@ -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);

	pc->flags = 0;



	/*

	 * We trust that only if there is a memcg associated with the page, it