linux-kernel - Re: [Patch v4 1/2] freezer: check OOM kill while being frozen

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Message-ID: <4394731.dfhKV5T3ox@vostro.rjw.lan>
Date:	Tue, 09 Sep 2014 01:59:06 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Patch v4 1/2] freezer: check OOM kill while being frozen

On Monday, September 08, 2014 04:29:24 PM Cong Wang wrote:
> On Mon, Sep 8, 2014 at 4:42 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > On Monday, September 08, 2014 04:16:15 PM Cong Wang wrote:
> >> On Mon, Sep 8, 2014 at 4:23 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >> >
> >> > The reason why it matters for the suspend-time freezing is that we freeze tasks
> >> > to take them out of the picture entirely until they are thawed.  Therefore we
> >> > can't allow them to go back to the picture just for a while until they are
> >> > killed.  Frozen tasks are not supposed to get back to the picture at all.
> >> >
> >>
> >>
> >> Ok, then checking TIF_MEMDIE is unsafe for PM freeze, we should
> >> keep the cgroup_freezing() test to make sure freeze request is from
> >> cgroup not PM. Question got answered. :)
> >
> > Do I think correctly that cgroups freezing and system suspend are
> > mutually exclusive?  If not, then this still is problematic.
> 
> Good point! Although rare, but it is possible we freeze a process both from
> cgroup and PM. Hmm, this means we have to explicitly exclude PM rather
> just checking cgroup freeze?

There's no way to do that currently as PM freezing is all-inclusive.

> Interesting, but I am not familiar with PM.

I'm wondering if the OOM killer might avoid killing frozen tasks instead?

Or there might be a "suspend" operation for the OOM killer that would be
run from a PM notifier to guaratee that the OOM killer would not mess up
with things during the entire system suspend (which surely is not quite
useful anyway).

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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