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

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Message-Id: <20090109113458.d9a1320d.nishimura@mxp.nes.nec.co.jp>
Date:	Fri, 9 Jan 2009 11:34:58 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	nishimura@....nes.nec.co.jp, 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 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 ?


Thanks,
Daisuke Nishimura.
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