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

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Date:	Mon, 24 Aug 2015 14:10:10 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
cc:	mhocko@...nel.org, 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 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, 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.
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