linux-kernel - [RFC][PATCH 5/6] memcg: remove unnecessary memory barrier.

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Message-ID: <4F72EF56.4030606@jp.fujitsu.com>
Date:	Wed, 28 Mar 2012 20:00:38 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	"linux-mm@...ck.org" <linux-mm@...ck.org>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Han Ying <yinghan@...gle.com>,
	Glauber Costa <glommer@...allels.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: [RFC][PATCH 5/6] memcg: remove unnecessary memory barrier.

Now, Used bit and a pointer to memory cgroup are set at once.
memory barrier for Used bit -> pc->mem_cgroup is not necessary.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
 mm/memcontrol.c |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 622fd2e..767bef3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1258,8 +1258,6 @@ mem_cgroup_get_reclaim_stat_from_page(struct page *page)
 	pc = lookup_page_cgroup(page);
 	if (!PageCgroupUsed(pc))
 		return NULL;
-	/* Ensure pc's mem_cgroup is visible after reading PCG_USED. */
-	smp_rmb();
 	mz = page_cgroup_zoneinfo(pc_to_mem_cgroup(pc), page);
 	return &mz->reclaim_stat;
 }
-- 
1.7.4.1


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