linux-kernel - Re: [patch -mm] mm, oom: add global access to memory reserves on livelock

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Message-ID: <20150825152650.GI6285@dhcp22.suse.cz>
Date:	Tue, 25 Aug 2015 17:26:51 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	akpm@...ux-foundation.org, mgorman@...e.de, hannes@...xchg.org,
	oleg@...hat.com, vbabka@...e.cz, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch -mm] mm, oom: add global access to memory reserves on
 livelock

On Mon 24-08-15 14:10:10, David Rientjes wrote:
> On Fri, 21 Aug 2015, Tetsuo Handa wrote:
> 
> > Why can't we think about choosing more OOM victims instead of granting access
> > to memory reserves?
> > 
> 
> We have no indication of which thread is holding a mutex that would need 
> to be killed, so we'd be randomly killing processes waiting for forward 
> progress.  A worst-case scenario would be the thread is OOM_DISABLE and we 
> kill every process on the system needlessly.  This problem obviously 
> occurs often enough that killing all userspace isnt going to be a viable 
> solution.
> 
> > Also, SysRq might not be usable under OOM because workqueues can get stuck.
> > The panic_on_oom_timeout was first proposed using a workqueue but was
> > updated to use a timer because there is no guarantee that workqueues work
> > as expected under OOM.
> > 
> 
> I don't know anything about a panic_on_oom_timeout,

You were CCed on the discussion
http://lkml.kernel.org/r/20150609170310.GA8990%40dhcp22.suse.cz

> but panicking would 
> only be a reasonable action if memory reserves were fully depleted.  That 
> could easily be dealt with in the page allocator so there's no timeout 
> involved.

As noted in other email. Just depletion is not a good indicator. The
system can still make a forward progress even when reserves are
depleted.

-- 
Michal Hocko
SUSE Labs
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