linux-kernel - Re: [RFC] [PATCH] Cgroup based OOM killer controller

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Date:	Mon, 26 Jan 2009 23:39:18 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, balbir@...ux.vnet.ibm.com,
	Nikanth Karthikesan <knikanth@...e.de>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org,
	Torvalds <torvalds@...ux-foundation.org>,
	Arve Hj?nnev?g <arve@...roid.com>,
	Evgeniy Polyakov <zbr@...emap.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Snook <csnook@...hat.com>,
	Linus@...p1.linux-foundation.org, Paul Menage <menage@...gle.com>
Subject: Re: [RFC] [PATCH] Cgroup based OOM killer controller

On Tue, 27 Jan 2009, KOSAKI Motohiro wrote:

> Confused.
> 
> As far as I know, people want the method of flexible cache treating.
> but oom seems less flexible than userland notification.
> 
> Why do you think notification is bad?
> 

There're a couple of proposals that have been discussed recently that 
share some functional behavior.

One is the cgroup oom notifier that allows you to attach a task to wait on 
an oom condition for a collection of tasks.  That allows userspace to 
respond to the condition by droping caches, adding nodes to a cpuset, 
elevating memory controller limits, sending a signal, etc.  It can also 
defer to the kernel oom killer as a last resort.

The other is /dev/mem_notify that allows you to poll() on a device file 
and be informed of low memory events.  This can include the cgroup oom 
notifier behavior when a collection of tasks is completely out of memory, 
but can also warn when such a condition may be imminent.  I suggested that 
this be implemented as a client of cgroups so that different handlers can 
be responsible for different aggregates of tasks.

I think the latter is a much more powerful tool and includes all the 
behavior of the former.  It preserves the oom killer as a last resort for 
the kernel and defers all preference killing or lowmem responses to 
userspace.
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