linux-kernel - Re: [PATCH 3/4] OOM, PM: OOM killed task shouldn't escape PM suspend

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Message-ID: <20141105160115.GA28226@dhcp22.suse.cz>
Date:	Wed, 5 Nov 2014 17:01:15 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cong Wang <xiyou.wangcong@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 3/4] OOM, PM: OOM killed task shouldn't escape PM suspend

On Wed 05-11-14 10:44:36, Tejun Heo wrote:
> On Wed, Nov 05, 2014 at 02:42:19PM +0100, Michal Hocko wrote:
> > On Wed 05-11-14 14:31:00, Michal Hocko wrote:
> > > On Wed 05-11-14 08:02:47, Tejun Heo wrote:
> > [...]
> > > > Also, why isn't this part of
> > > > oom_killer_disable/enable()?  The way they're implemented is really
> > > > silly now.  It just sets a flag and returns whether there's a
> > > > currently running instance or not.  How were these even useful? 
> > > > Why can't you just make disable/enable to what they were supposed to
> > > > do from the beginning?
> > > 
> > > Because then we would block all the potential allocators coming from
> > > workqueues or kernel threads which are not frozen yet rather than fail
> > > the allocation.
> > 
> > After thinking about this more it would be doable by using trylock in
> > the allocation oom path. I will respin the patch. The API will be
> > cleaner this way.
> 
> In disable, block new invocations of OOM killer and then drain the
> in-progress ones.  This is a common pattern, isn't it?

I am not sure I am following. With the latest patch OOM path is no
longer blocked by the PM (aka oom_killer_disable()). Allocations simply
fail if the read_trylock fails.
oom_killer_disable is moved before tasks are frozen and it will wait for
all on-going OOM killers on the write lock. OOM killer is enabled again
on the resume path.

-- 
Michal Hocko
SUSE Labs
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