linux-kernel - Re: [patch 7/8] mm: memcg: modify PageCgroupAcctLRU non-atomically

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Message-ID: <20111124085532.GB6843@cmpxchg.org>
Date:	Thu, 24 Nov 2011 09:55:33 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Balbir Singh <bsingharora@...il.com>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 7/8] mm: memcg: modify PageCgroupAcctLRU non-atomically

On Thu, Nov 24, 2011 at 09:09:15AM +0900, KAMEZAWA Hiroyuki wrote:
> On Wed, 23 Nov 2011 16:42:30 +0100
> Johannes Weiner <hannes@...xchg.org> wrote:
> 
> > From: Johannes Weiner <jweiner@...hat.com>
> > 
> > This bit is protected by zone->lru_lock, there is no need for locked
> > operations when setting and clearing it.
> > 
> > Signed-off-by: Johannes Weiner <jweiner@...hat.com>
> 
> This atomic ops are for avoiding race with other ops as lock_page_cgroup().
> Or other Set/ClearPageCgroup....
> 
> Do I misunderstand atomic ops v.s. non-atomic ops race ?

Nope, you are spot-on.  I'm the cretin. ;-) See my reply to Hugh's
email.
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