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SubjectRe: [RFC][0/3] Virtual address space control for cgroups
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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