linux-kernel - Re: [PATCH 2/6 v4] memcg: simplify move

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Message-Id: <20120214174442.3efcb22c.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 14 Feb 2012 17:44:42 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Greg Thelen <gthelen@...gle.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Ying Han <yinghan@...gle.com>, Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 2/6 v4] memcg: simplify move_account() check

On Mon, 13 Feb 2012 23:21:34 -0800
Greg Thelen <gthelen@...gle.com> wrote:

> On Mon, Feb 13, 2012 at 7:07 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@...fujitsu.com> wrote:
> > From 9cdb3b63dc8d08cc2220c54c80438c13433a0d12 Mon Sep 17 00:00:00 2001
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > Date: Thu, 2 Feb 2012 10:02:39 +0900
> > Subject: [PATCH 2/6] memcg: simplify move_account() check.
> >
> > In memcg, for avoiding take-lock-irq-off at accessing page_cgroup,
> > a logic, flag + rcu_read_lock(), is used. This works as following
> >
> >     CPU-A                     CPU-B
> >                             rcu_read_lock()
> >    set flag
> >                             if(flag is set)
> >                                   take heavy lock
> >                             do job.
> >    synchronize_rcu()        rcu_read_unlock()
> 
> I assume that CPU-A will take heavy lock after synchronize_rcu() when
> updating variables read by CPU-B.
> 
Ah, yes. I should wrote that.

> >  memcontrol.c |   65 ++++++++++++++++++++++-------------------------------------
> >  1 file changed, 25 insertions(+), 40 deletions(-)
> >
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> Acked-by: Greg Thelen <gthelen@...gle.com>
> 

Thank you!.

-Kame

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