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Date: Fri, 29 May 2015 08:55:04 +0200
From: Michal Hocko <mhocko@suse.cz>
Subject: Re: [PATCH] memcg: do not call reclaim if !__GFP_WAIT
Message-ID: <20150529065504.GA22728@dhcp22.suse.cz>
References: <1432833966-25538-1-git-send-email-vdavydov@parallels.com>
 <20150528125934.198f57db4c5daf19dd15b184@linux-foundation.org>
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To: Andrew Morton <akpm@linux-foundation.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Johannes Weiner <hannes@cmpxchg.org>

On Thu 28-05-15 12:59:34, Andrew Morton wrote:
> On Thu, 28 May 2015 20:26:06 +0300 Vladimir Davydov <vdavydov@parallels.com> wrote:
> 
> > When trimming memcg consumption excess (see memory.high), we call
> > try_to_free_mem_cgroup_pages without checking if we are allowed to sleep
> > in the current context, which can result in a deadlock. Fix this.
> 
> Why does it deadlock?  try_to_free_mem_cgroup_pages() is passed the
> gfp_mask and should honour its __GFP_WAIT setting?

The only instance of __GFP_WAIT check in vmscan code is in zone_reclaim.
Page allocations and memcg reclaim avoids calling reclaim if __GFP_WAIT
is not set. Maybe we can move the check to do_try_to_free_pages?

-- 
Michal Hocko
SUSE Labs

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