linux-kernel - Re: Improving OOM killer

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Message-ID: <alpine.DEB.2.00.1002041410300.16391@chino.kir.corp.google.com>
Date:	Thu, 4 Feb 2010 14:14:50 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Rik van Riel <riel@...hat.com>
cc:	Lubos Lunak <l.lunak@...e.cz>,
	Balbir Singh <balbir@...ux.vnet.ibm.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>, Jiri Kosina <jkosina@...e.cz>
Subject: Re: Improving OOM killer

On Thu, 4 Feb 2010, Rik van Riel wrote:

> > Keep in mind that we're in the oom killer here, though.  So we're out of
> > memory and we need to kill something; should Apache, Oracle, and postgres
> > not be penalized for their cost of running by factoring in something like
> > this?
> 
> No, they should not.
> 
> The goal of the OOM killer is to kill some process, so the
> system can continue running and automatically become available
> again for whatever workload the system was running.
> 
> Killing the parent process of one of the system daemons does
> not achieve that goal, because you now caused a service to no
> longer be available.
> 

The system daemon wouldn't be killed, though.  You're right that this 
heuristic would prefer the system daemon slightly more as a result of the 
forkbomb penalty, but the oom killer always attempts to sacrifice a child 
with a seperate mm before killing the selected task.  Since the forkbomb 
heuristic only adds up those children with seperate mms, we're guaranteed 
to not kill the daemon itself.
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