Re: [PATCH] KVM simplified virtio balloon driver

[Dor Laor <dor.laor-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Thu, 2008-01-17 at 11:25 +0100, Martin Schwidefsky wrote:
> > 
> > Another idea: Martin added an oom notifier to the cmm driver. Before the 
> > oom-killer kicks in cmm will try to free 256 pages. I think your virtio 
> > balloon driver should do the same - it seems to be the correct tradeoff. 
> 
> Nod, you definitly want to add an oom notifier. If 256 pages is the
> correct number of pages to free is debatable. We have seen long delays
> for a process that quickly eats up memory if there are lots of pages in
> the balloon. The problem is that the memory management tries hard to
> find memory until it decides to oom kill a process, only to be stopped
> in the last second by the oom notifier. The 1MB is quickly eaten up
> again so the whole things starts again. The profile of such a scenario
> shows that almost all cpu is burned in the page reclaim code.
> 

Seconded, in that case we can add a config space notification from the
guest to the host that will be triggered by the oom.
The host will get this notification and will decide whether to allow the
guest to deflate the balloon or to keep the current balloon size because
the whole host is over committed.
Regards,
Dor.


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