Messages in this thread Patch in this message | | | From | Johannes Weiner <> | Subject | [patch 09/12] mm: memcontrol: remove ordering between pc->mem_cgroup and PageCgroupUsed | Date | Mon, 16 Jun 2014 15:54:29 -0400 |
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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 38c5d72f3ebe ("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: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Michal Hocko <mhocko@suse.cz> --- mm/memcontrol.c | 9 --------- 1 file changed, 9 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 3726f6774860..1cde6e2b33d9 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2801,14 +2801,6 @@ 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. - */ - smp_wmb(); SetPageCgroupUsed(pc); if (lrucare) { @@ -3490,7 +3482,6 @@ 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; } __this_cpu_sub(memcg->stat->count[MEM_CGROUP_STAT_RSS_HUGE], -- 2.0.0
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