From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755761AbaFRUlU (ORCPT ); Wed, 18 Jun 2014 16:41:20 -0400 Received: from zene.cmpxchg.org ([85.214.230.12]:37571 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755647AbaFRUlL (ORCPT ); Wed, 18 Jun 2014 16:41:11 -0400 From: Johannes Weiner To: Andrew Morton Cc: Michal Hocko , Hugh Dickins , Tejun Heo , Vladimir Davydov , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [patch 10/13] mm: memcontrol: remove ordering between pc->mem_cgroup and PageCgroupUsed Date: Wed, 18 Jun 2014 16:40:42 -0400 Message-Id: <1403124045-24361-11-git-send-email-hannes@cmpxchg.org> X-Mailer: git-send-email 2.0.0 In-Reply-To: <1403124045-24361-1-git-send-email-hannes@cmpxchg.org> References: <1403124045-24361-1-git-send-email-hannes@cmpxchg.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.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 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 Acked-by: Michal Hocko --- mm/memcontrol.c | 9 --------- 1 file changed, 9 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index d2b8429002c0..199bd50359ad 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -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. - */ - smp_wmb(); SetPageCgroupUsed(pc); 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; } __this_cpu_sub(memcg->stat->count[MEM_CGROUP_STAT_RSS_HUGE], -- 2.0.0