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

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Message-ID: <502BABCF.7020608@parallels.com>
Date:	Wed, 15 Aug 2012 18:01:51 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Michal Hocko <mhocko@...e.cz>
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 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.

How about we change the following code in mem_cgroup_do_charge:

        if (gfp_mask & __GFP_NORETRY)
                return CHARGE_NOMEM;

to:

        if ((gfp_mask & __GFP_NORETRY) || (gfp_mask & __GFP_ATOMIC))
                return CHARGE_NOMEM;

?

Would this take care of the issue ?
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