linux-kernel - Re: [RFC 0/4] OOM vs PM freezer fixes

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Date:	Tue, 18 Nov 2014 22:08:33 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	linux-pm@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"\\\"Rafael J. Wysocki\\\"" <rjw@...ysocki.net>,
	David Rientjes <rientjes@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: [RFC 0/4] OOM vs PM freezer fixes

On Fri 14-11-14 15:14:19, Tejun Heo wrote:
> On Wed, Nov 12, 2014 at 07:58:48PM +0100, Michal Hocko wrote:
> > Hi,
> > here is another take at OOM vs. PM freezer interaction fixes/cleanups.
> > First three patches are fixes for an unlikely cases when OOM races with
> > the PM freezer which should be closed completely finally. The last patch
> > is a simple code enhancement which is not needed strictly speaking but
> > it is nice to have IMO.
> > 
> > Both OOM killer and PM freezer are quite subtle so I hope I haven't
> > missing anything. Any feedback is highly appreciated. I am also
> > interested about feedback for the used approach. To be honest I am not
> > really happy about spreading TIF_MEMDIE checks into freezer (patch 1)
> > but I didn't find any other way for detecting OOM killed tasks.
> 
> I really don't get why this is structured this way.  Can't you just do
> the following?

Well, I liked how simple this was and localized at the only place which
matters. When I was thinking about a solution which you are describing
below it was more complicated and more subtle (e.g. waiting for an OOM
victim might be tricky if it stumbles over a lock which is held by a
frozen thread which uses try_to_freeze_unsafe). Anyway I gave it another
try and will post the two patches as a reply to this email. I hope the
both interface and implementation is cleaner.

> 1. Freeze all freezables.  Don't worry about PF_MEMDIE.
> 
> 2. Disable OOM killer.  This should be contained in the OOM killer
>    proper.  Lock out the OOM killer and disable it.
> 
> 3. At this point, we know that no one will create more freezable
>    threads and no new process will be OOM kliled.  Wait till there's
>    no process w/ PF_MEMDIE set.
> 
> There's no reason to lock out or disable OOM killer while the system
> is not in the quiescent state, which is a big can of worms.  Bring
> down the system to the quiescent state, disable the OOM killer and
> then drain PF_MEMDIEs.

-- 
Michal Hocko
SUSE Labs
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