linux-kernel - Re: [PATCH v2 06/11] memcg: kmem controller infrastructure

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Message-ID: <20120815142338.GL23985@dhcp22.suse.cz>
Date:	Wed, 15 Aug 2012 16:23:38 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Glauber Costa <glommer@...allels.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	cgroups@...r.kernel.org, devel@...nvz.org,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	kamezawa.hiroyu@...fujitsu.com, Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v2 06/11] memcg: kmem controller infrastructure

On Wed 15-08-12 18:01:51, Glauber Costa wrote:
> On 08/15/2012 05:09 PM, Michal Hocko wrote:
> > On Wed 15-08-12 13:42:24, Glauber Costa wrote:
> > [...]
> >>>> +
> >>>> +	ret = 0;
> >>>> +
> >>>> +	if (!memcg)
> >>>> +		return ret;
> >>>> +
> >>>> +	_memcg = memcg;
> >>>> +	ret = __mem_cgroup_try_charge(NULL, gfp, delta / PAGE_SIZE,
> >>>> +	    &_memcg, may_oom);
> >>>
> >>> This is really dangerous because atomic allocation which seem to be
> >>> possible could result in deadlocks because of the reclaim. 
> >>
> >> Can you elaborate on how this would happen?
> > 
> > Say you have an atomic allocation and we hit the limit so we get either
> > to reclaim which can sleep or to oom which can sleep as well (depending
> > on the oom_control).
> > 
> 
> I see now, you seem to be right.

No I am not because it seems that I am really blind these days...
We were doing this in mem_cgroup_do_charge for ages:
	if (!(gfp_mask & __GFP_WAIT))
                return CHARGE_WOULDBLOCK;

/me goes to hide and get with further feedback with a clean head.

Sorry about that.
-- 
Michal Hocko
SUSE Labs
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