linux-kernel - Re: [PATCH] memcg: do not call reclaim if !__GFP

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Date:	Fri, 29 May 2015 08:55:04 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vladimir Davydov <vdavydov@...allels.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] memcg: do not call reclaim if !__GFP_WAIT

On Thu 28-05-15 12:59:34, Andrew Morton wrote:
> On Thu, 28 May 2015 20:26:06 +0300 Vladimir Davydov <vdavydov@...allels.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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