linux-kernel - Re: [RFC][PATCH 1/4] memcg: fix for mem_cgroup_get_reclaim_stat_from

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Message-Id: <20090109114155.75fd61fc.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 9 Jan 2009 11:41:55 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	Li Zefan <lizf@...fujitsu.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, balbir@...ux.vnet.ibm.com,
	menage@...gle.com
Subject: Re: [RFC][PATCH 1/4] memcg: fix for
 mem_cgroup_get_reclaim_stat_from_page

On Fri, 9 Jan 2009 11:34:58 +0900
Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:

> On Fri, 9 Jan 2009 10:05:31 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > On Fri, 09 Jan 2009 08:57:59 +0800
> > Li Zefan <lizf@...fujitsu.com> wrote:
> > 
> > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > > index e2996b8..62e69d8 100644
> > > > --- a/mm/memcontrol.c
> > > > +++ b/mm/memcontrol.c
> > > > @@ -559,6 +559,10 @@ mem_cgroup_get_reclaim_stat_from_page(struct page *page)
> > > >  		return NULL;
> > > >  
> > > >  	pc = lookup_page_cgroup(page);
> > > > +	smp_rmb();
> > > 
> > > It is better to add a comment to explain this smp_rmb. I think it's recommended
> > > that every memory barrier has a comment.
> > > 
> > Ah, yes. good point.
> > 
> > Maybe text like this
> > /*
> >  * Used bit is set without atomic ops but after smp_wmb().
> >  * For making pc->mem_cgroup visible, insert smp_rmb() here.
> >  */
> > 
> OK. I'll add this comment.
> 
> BTW, mem_cgroup_rotate_lru_list and mem_cgroup_add_lru_list have similar code.
> (mem_cgroup_add_lru_list has some comment already.)
> Should I update them too ?
> 
please :) it's helpful. Sorry for my too short comment on orignal patch.

-Kame

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