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Commit a840cda6 authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
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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: 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
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+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