[openstack-dev] [nova] [RFC] how to enable xbzrle compress for live migration

Daniel P. Berrange berrange at redhat.com
Fri Nov 27 12:23:30 UTC 2015


On Fri, Nov 27, 2015 at 12:17:06PM +0000, Koniszewski, Pawel wrote:
> > -----Original Message-----
> > > > Doing this though, we still need a solution to the host OOM scenario
> > > > problem. We can't simply check free RAM at start of migration and
> > > > see if there's enough to spare for compression cache, as the
> > > > schedular can spawn a new guest on the compute host at any time,
> > > > pushing us into OOM. We really need some way to indicate that there
> > > > is a (potentially very large) extra RAM overhead for the guest during
> > migration.
> 
> What about CPU? We might end up with live migration that degrades
> performance of other VMs on source and/or destination node. AFAIK
> CPUs are heavily oversubscribed in many cases and this does not help.
> I'm not sure that this thing fits into Nova as it requires resource
> monitoring.

Nova already has the ability to set CPU usage tuning rules against
each VM. Since the CPU overhead is attributed to the QEMU process,
these existing tuning rules will apply. So there would only be
impact on other VMs, if you do not have any CPU tuning rules set
in Nova.


Regards,
Daniel
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