linux-kernel - Re: [RFC][PATCH -mmotm 1/4] memcg: don't trigger oom at page migration

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Date:	Sat, 6 Dec 2008 11:47:57 +0900
From:	Daisuke Nishimura <d-nishimura@....biglobe.ne.jp>
To:	balbir@...ux.vnet.ibm.com
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Paul Menage <menage@...gle.com>, d-nishimura@....biglobe.ne.jp,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [RFC][PATCH -mmotm 1/4] memcg: don't trigger oom at page
 migration

On Fri, 5 Dec 2008 19:09:26 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> * Daisuke Nishimura <nishimura@....nes.nec.co.jp> [2008-12-05 21:23:04]:
> 
> > I think triggering OOM at mem_cgroup_prepare_migration would be just a bit
> > overkill.
> > Returning -ENOMEM would be enough for mem_cgroup_prepare_migration.
> > The caller would handle the case anyway.
> > 
> > Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> > ---
> >  mm/memcontrol.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 4dbce1d..50ee1be 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -1330,7 +1330,7 @@ int mem_cgroup_prepare_migration(struct page *page, struct mem_cgroup **ptr)
> >  	unlock_page_cgroup(pc);
> > 
> >  	if (mem) {
> > -		ret = mem_cgroup_try_charge(NULL, GFP_KERNEL, &mem);
> > +		ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, &mem, false);
> >  		css_put(&mem->css);
> >  	}
> >  	*ptr = mem;
> >
> 
> Seems reasonable to me. A comment indicating or adding a noreclaim
> wrapper around __mem_cgroup_try_charge to indicate that no reclaim
> will take place will be nice.
> 
Ah.. this flag to __mem_cgroup_try_charge doesn't mean "don't reclaim"
but "don't cause oom after it tried to free memory but couldn't
free enough memory after all".

Thanks,
Daisuke Nishimura.

> Acked-by: Balbir Singh <balbir@...ux.vnet.ibm.com> 
> 
> -- 
> 	Balbir
> 
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