linux-kernel - Re: Improving OOM killer

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Date:	Thu, 4 Feb 2010 13:39:08 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Jiri Kosina <jkosina@...e.cz>
cc:	Lubos Lunak <l.lunak@...e.cz>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: Improving OOM killer

On Thu, 4 Feb 2010, Jiri Kosina wrote:

> Why does OOM killer care about forkbombs *at all*?
> 

Because the cumulative effects of a forkbomb are detrimental to the 
system and the badness() heursitic favors large memory consumers very 
heavily.  Thus, the forkbomb is never really a strong candidate for oom 
kill since the parent may consume very little memory itself and meanwhile 
KDE or another large memory consumer will get innocently killed instead as 
a result.

> If we really want kernel to detect forkbombs (*), we'd have to establish 
> completely separate infrastructure for that (with its own knobs for tuning 
> and possibilities of disabling it completely).
> 

That's what we're trying to do, we can look at the shear number of 
children that the parent has forked and check for it to be over a certain 
"forkbombing threshold" (which, yes, can be tuned from userspace), the 
uptime of those children, their resident set size, etc., to attempt to 
find a sane heuristic that penalizes them.
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