From: Johannes Weiner <han...@cmpxchg.org> 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 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 <han...@cmpxchg.org> Acked-by: Michal Hocko <mho...@suse.cz> Cc: Hugh Dickins <hu...@google.com> Cc: Tejun Heo <t...@kernel.org> Cc: Vladimir Davydov <vdavy...@parallels.com> Signed-off-by: Andrew Morton <a...@linux-foundation.org> Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> https://jira.sw.ru/browse/PSBM-51558 (cherry picked from commit 9a2385eef9f28fb5260c48c45fc8fe01f1da70a6) Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com> --- mm/memcontrol.c | 9 --------- 1 file changed, 9 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 9cf702c..84687f3 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2989,14 +2989,6 @@ 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) { @@ -3536,7 +3528,6 @@ 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], -- 2.7.3 _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel