Commit 9a2385ee authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds

mm: memcontrol: remove ordering between pc->mem_cgroup and PageCgroupUsed

There is a write barrier between setting pc->mem_cgroup and
PageCgroupUsed, which was added to allow LRU operations to lookup the
memcg LRU list of a page without acquiring the page_cgroup lock.

But ever since commit 38c5d72f ("memcg: simplify LRU handling by new
rule"), pages are ensured to be off-LRU while charging, so nobody else
is changing LRU state while pc->mem_cgroup is being written, and there
are no read barriers anymore.

Remove the unnecessary write barrier.
Signed-off-by: default avatarJohannes Weiner <>
Acked-by: default avatarMichal Hocko <>
Cc: Hugh Dickins <>
Cc: Tejun Heo <>
Cc: Vladimir Davydov <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 05b84301
......@@ -2795,14 +2795,6 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
pc->mem_cgroup = memcg;
* We access a page_cgroup asynchronously without lock_page_cgroup().
* Especially when a page_cgroup is taken from a page, pc->mem_cgroup
* is accessed after testing USED bit. To make pc->mem_cgroup visible
* before USED bit, we need memory barrier here.
* See mem_cgroup_add_lru_list(), etc.
if (lrucare) {
......@@ -3483,7 +3475,6 @@ void mem_cgroup_split_huge_fixup(struct page *head)
for (i = 1; i < HPAGE_PMD_NR; i++) {
pc = head_pc + i;
pc->mem_cgroup = memcg;
smp_wmb();/* see __commit_charge() */
pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;
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