linux-kernel - Re: [PATCH 2/6] mm,oom: don't abort on exiting processes when selecting a victim.

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Date:	Wed, 17 Feb 2016 23:39:47 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	mhocko@...nel.org
Cc:	akpm@...ux-foundation.org, rientjes@...gle.com, mgorman@...e.de,
	oleg@...hat.com, torvalds@...ux-foundation.org, hughd@...gle.com,
	andrea@...nel.org, riel@...hat.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] mm,oom: don't abort on exiting processes when selecting a victim.

Michal Hocko wrote:
> On Wed 17-02-16 22:07:31, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > On Wed 17-02-16 19:30:41, Tetsuo Handa wrote:
> > > > >From 22bd036766e70f0df38c38f3ecc226e857d20faf Mon Sep 17 00:00:00 2001
> > > > From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> > > > Date: Wed, 17 Feb 2016 16:30:59 +0900
> > > > Subject: [PATCH 2/6] mm,oom: don't abort on exiting processes when selecting a victim.
> > > > 
> > > > Currently, oom_scan_process_thread() returns OOM_SCAN_ABORT when there
> > > > is a thread which is exiting. But it is possible that that thread is
> > > > blocked at down_read(&mm->mmap_sem) in exit_mm() called from do_exit()
> > > > whereas one of threads sharing that memory is doing a GFP_KERNEL
> > > > allocation between down_write(&mm->mmap_sem) and up_write(&mm->mmap_sem)
> > > > (e.g. mmap()). Under such situation, the OOM killer does not choose a
> > > > victim, which results in silent OOM livelock problem.
> > > 
> > > Again, such a thread/task will have fatal_signal_pending and so have
> > > access to memory reserves. So the text is slightly misleading imho.
> > > Sure if the memory reserves are depleted then we will not move on but
> > > then it is not clear whether the current patch helps either.
> > 
> > I don't think so.
> > Please see http://lkml.kernel.org/r/201602151958.HCJ48972.FFOFOLMHSQVJtO@I-love.SAKURA.ne.jp .
> 
> I have missed this one. Reading...
> 
> Hmm, so you are not referring to OOM killed task but naturally exiting
> thread which is racing with the OOM killer. I guess you have a point
> there! Could you update the changelog with the above example and repost
> please?
> 
Yes and I resent that patch as v2.

I think that the same problem exists for any task_will_free_mem()-based
optimizations. Can we eliminate them because these optimized paths are not
handled by the OOM reaper which means that we have no means other than
"[PATCH 5/6] mm,oom: Re-enable OOM killer using timers." ?