linux-kernel - Re: [PATCH 10/10] mm, oom: hide mm which is shared with kthread or global init

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Date:	Wed, 20 Jul 2016 08:29:12 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Rientjes <rientjes@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/10] mm, oom: hide mm which is shared with kthread or
 global init

On Tue 19-07-16 16:27:59, Andrew Morton wrote:
> On Tue, 19 Jul 2016 14:05:39 +0200 Michal Hocko <mhocko@...nel.org> wrote:
> 
> > > After this patch we should guarantee a forward progress for the OOM
> > > killer even when the selected victim is sharing memory with a kernel
> > > thread or global init.
> > 
> > Could you replace the last two paragraphs with the following. Tetsuo
> > didn't like the guarantee mentioned there because that is a too strong
> > statement as find_lock_task_mm might not find any mm and so we still
> > could end up looping on the oom victim if it gets stuck somewhere in
> > __mmput. This particular patch didn't aim at closing that case. Plugging
> > that hole is planned later after the next upcoming merge window closes.
> > 
> > "
> > In order to help a forward progress for the OOM killer, make sure
> > that this really rare cases will not get into the way and hide
> > the mm from the oom killer by setting MMF_OOM_REAPED flag for it.
> > oom_scan_process_thread will ignore any TIF_MEMDIE task if it has
> > MMF_OOM_REAPED flag set to catch these oom victims.
> > 		        
> > After this patch we should guarantee a forward progress for the OOM
> > killer even when the selected victim is sharing memory with a kernel
> > thread or global init as long as the victims mm is still alive.
> > "
> 
> I tweaked it a bit:
> 
> : In order to help forward progress for the OOM killer, make sure that
> : this really rare case will not get in the way - we do this by hiding
> : the mm from the oom killer by setting MMF_OOM_REAPED flag for it. 
> : oom_scan_process_thread will ignore any TIF_MEMDIE task if it has
> : MMF_OOM_REAPED flag set to catch these oom victims.
> : 
> : After this patch we should guarantee forward progress for the OOM
> : killer even when the selected victim is sharing memory with a kernel
> : thread or global init as long as the victims mm is still alive.

Sounds good to me. Thanks!

-- 
Michal Hocko
SUSE Labs