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>
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@ -3407,12 +3407,13 @@ void __memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg,
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memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
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return;
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}
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/*
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* The page is freshly allocated and not visible to any
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* outside callers yet. Set up pc non-atomically.
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*/
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pc = lookup_page_cgroup(page);
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lock_page_cgroup(pc);
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pc->mem_cgroup = memcg;
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SetPageCgroupUsed(pc);
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unlock_page_cgroup(pc);
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pc->flags = PCG_USED;
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}
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void __memcg_kmem_uncharge_pages(struct page *page, int order)
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@ -3422,19 +3423,11 @@ void __memcg_kmem_uncharge_pages(struct page *page, int order)
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pc = lookup_page_cgroup(page);
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/*
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* Fast unlocked return. Theoretically might have changed, have to
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* check again after locking.
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*/
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if (!PageCgroupUsed(pc))
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return;
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lock_page_cgroup(pc);
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if (PageCgroupUsed(pc)) {
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memcg = pc->mem_cgroup;
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ClearPageCgroupUsed(pc);
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}
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unlock_page_cgroup(pc);
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pc->flags = 0;
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/*
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* We trust that only if there is a memcg associated with the page, it
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