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

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Message-Id: <20160719162759.e391c685db7a8de30b79320c@linux-foundation.org>
Date:	Tue, 19 Jul 2016 16:27:59 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michal Hocko <mhocko@...nel.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 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.