[Devel] Re: [ANNOUNCE] first stable release of OpenVZ kernel virtualization solution

[Ingo Molnar]

* Kirill Korotaev <dev at sw.ru> wrote:

> >interesting. Have you tested the corner case of: 'one lowprio VPS is 
> >swapping like mad', how it affects highprio VPSs?

> Both VPSs have a single page cache. So if one VPS is swapping like hell, 
>  it's neighbour is swapping as well. This naturally means that node is 
> out of memory since you created overcommitted configuration.
> It is up to you whether:
> - to limit the offender
> - kill the offender
> - migrate the high-prio or low-prio VPS to another node
> - add RAM :)

well, the other solution is to let certain instances overcommit 
userspace RAM, and to just use a swap device for that scenario. An admin 
can fix or shut down the offender, but other, more important instances 
would still be up and running. Hard limits have other problems: they are 
hard failures, instead of graceful failures.

by 'swapping madly' i dont mean lowmem pressure, but plain userspace VM 
pressure. I fear it's not flexible enough to not allow for that. I.e. it 
would be nice to extend the beancounters to let userspace to _swap_ 
instead of exposing it to a hard limit.

	Ingo