Message-ID: <47DDE187.70109@linux.vnet.ibm.com>
Date: Mon, 17 Mar 2008 08:42:07 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
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Organization: IBM
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To: Paul Menage <menage@google.com>
CC: linux-mm@kvack.org, Hugh Dickins <hugh@veritas.com>,
       Sudhir Kumar <skumar@linux.vnet.ibm.com>,
       YAMAMOTO Takashi <yamamoto@valinux.co.jp>, lizf@cn.fujitsu.com,
       linux-kernel@vger.kernel.org, taka@valinux.co.jp,
       David Rientjes <rientjes@google.com>,
       Pavel Emelianov <xemul@openvz.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [RFC][0/3] Virtual address space control for cgroups
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Paul Menage wrote:
> On Mon, Mar 17, 2008 at 9:50 AM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
>>  I am yet to measure the performance overhead of the accounting checks. I'll try
>>  and get started on that today. I did not consider making it a separate system,
>>  because I suspect that anybody wanting memory control would also want address
>>  space control (for the advantages listed in the documentation).
> 
> I'm a counter-example to your suspicion :-)
> 
> Trying to control virtual address space is a complete nightmare in the
> presence of anything that uses large sparsely-populated mappings
> (mmaps of large files, or large sparse heaps such as the JVM uses.)
> 

Not really. Virtual limits are more gentle than an OOM kill that can occur if
the cgroup runs out of memory. Please also see
http://linux-vserver.org/Memory_Limits

> If we want to control the effect of swapping, the right way to do it
> is to control disk I/O, and ensure that the swapping is accounted to
> that. Or simply just not give apps much swap space.

Yes, a disk I/O and swap I/O controller are being developed (not by us, but
others in the community). How does one restrict swap space for a particular
application? I can think of RLIMIT_AS for a process and something similar to
what I've posted for cgroups. Not enabling swap is an option, but not very
practical IMHO.

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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