linux-kernel - Re: [PATCH v5 06/14] memcg: kmem controller infrastructure

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Message-ID: <alpine.DEB.2.00.1210191331400.17804@chino.kir.corp.google.com>
Date:	Fri, 19 Oct 2012 13:34:04 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Glauber Costa <glommer@...allels.com>
cc:	linux-mm@...ck.org, cgroups@...r.kernel.org,
	Mel Gorman <mgorman@...e.de>, Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>, devel@...nvz.org,
	linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v5 06/14] memcg: kmem controller infrastructure

On Fri, 19 Oct 2012, Glauber Costa wrote:

> >>> What about gfp & __GFP_FS?
> >>>
> >>
> >> Do you intend to prevent or allow OOM under that flag? I personally
> >> think that anything that accepts to be OOM-killed should have GFP_WAIT
> >> set, so that ought to be enough.
> >>
> > 
> > The oom killer in the page allocator cannot trigger without __GFP_FS 
> > because direct reclaim has little chance of being very successful and 
> > thus we end up needlessly killing processes, and that tends to happen 
> > quite a bit if we dont check for it.  Seems like this would also happen 
> > with memcg if mem_cgroup_reclaim() has a large probability of failing?
> > 
> 
> I can indeed see tests for GFP_FS in some key locations in mm/ before
> calling the OOM Killer.
> 
> Should I test for GFP_IO as well?

It's not really necessary, if __GFP_IO isn't set then it wouldn't make 
sense for __GFP_FS to be set.

> If the idea is preventing OOM to
> trigger for allocations that can write their pages back, how would you
> feel about the following test:
> 
> may_oom = (gfp & GFP_KERNEL) && !(gfp & __GFP_NORETRY) ?
> 

I would simply copy the logic from the page allocator and only trigger oom 
for __GFP_FS and !__GFP_NORETRY.
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