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

On 11.06.2015 10:13, Daniel P. Berrange wrote: > 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. Unless hugepages are requested for guest NUMA nodes. In that case memory-backend-file object is required. From my investigation, this seems to be the case.