linux-kernel - Re: [PATCH v3] oom-kill: add lowmem usage aware oom kill handling

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Message-ID: <alpine.DEB.2.00.1002010228360.12764@chino.kir.corp.google.com>
Date:	Mon, 1 Feb 2010 02:33:55 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Vedran Furac <vedran.furac@...il.com>
cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	minchan.kim@...il.com, Balbir Singh <balbir@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v3] oom-kill: add lowmem usage aware oom kill handling

On Sun, 31 Jan 2010, Vedran Furac wrote:

> > You snipped the code segment where I demonstrated that the selected task 
> > for oom kill is not necessarily the one chosen to die: if there is a child 
> > with disjoint memory that is killable, it will be selected instead.  If 
> > Xorg or sshd is being chosen for kill, then you should investigate why 
> > that is, but there is nothing random about how the oom killer chooses 
> > tasks to kill.
> 
> I know that it isn't random, but it sure looks like that to the end user
> and I use it to emphasize the problem. And about me investigating, that
> simply not possible as I am not a kernel hacker who understands the code
> beyond the syntax level. I can only point to the problem in hope that
> someone will fix it.
> 

Disregarding the opportunity that userspace has to influence the oom 
killer's selection for a moment, it really tends to favor killing tasks 
that are the largest in size.  Tasks that typically get the highest 
badness score are those that have the highest mm->total_vm, it's that 
simple.  There are definitely cornercases where the first generation 
children have a strong influence, but they are often killed either as a 
result of themselves being a thread group leader with seperate memory from 
the parent or as the result of the oom killer killing a task with seperate 
memory before the selected task.  It's completely natural for the oom 
killer to select bash, for example, when in actuality it will kill a 
memory leaker that has a high badness score as a result of the logic in 
oom_kill_process().

If you have specific logs that you'd like to show, please enable 
/proc/sys/vm/oom_dump_tasks and respond with them in another message with 
that data inline.
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