[libvirt] Problem with setting up KVM guests to use HugePages

[Daniel P. Berrange]

On Wed, Jun 10, 2015 at 09:20:40PM +0000, Vivi L wrote:
> Michal Privoznik <mprivozn <at> redhat.com> writes:
> 
> > 
> > On 10.06.2015 01:05, Vivi L wrote:
> > > Kashyap Chamarthy <kchamart <at> redhat.com> writes:
> > > 
> > > 
> > >> You might want re-test by explicitly setting the 'page' element and
> > >> 'size' attribute? From my test, I had something like this:
> > >>
> > >>     $ virsh dumpxml f21-vm | grep hugepages -B3 -A2 
> > >>       <memory unit='KiB'>2000896</memory>
> > >>       <currentMemory unit='KiB'>2000000</currentMemory>
> > >>       <memoryBacking>
> > >>         <hugepages>
> > >>           <page size='2048' unit='KiB' nodeset='0'/>
> > >>         </hugepages>
> > >>       </memoryBacking>
> > >>       <vcpu placement='static'>8</vcpu>
> > >>
> > >> I haven't tested this exhaustively, but some basic test notes here:
> > >>
> > >>     https://kashyapc.fedorapeople.org/virt/test-hugepages-with-libvirt.txt
> > > 
> > > Current QEMU does not support setting <page> element. Could it be the 
> > > cause of my aforementioned problem?
> > > 
> > > unsupported configuration: huge pages per NUMA node are not supported 
> > > with this QEMU
> > > 
> > 
> > So this is explanation why the memory for you guest is not backed by
> > hugepages.
> 
> I thought setting hugepages per NUMA node is a nice-to-have feature. 
> Is it required to enable the use of hugepages for the guest?

No, it should not be mandatory. You should be able to use

  <memoryBacking>
        <hugepages/>
  </memoryBacking>

With pretty much any KVM/QEMU version that exists. If that's
broken then its a libvit bug.

Regards,
Daniel
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