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

On Thu, Jun 11, 2015 at 10:27:05AM +0200, Michal Privoznik wrote: > 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. memory-backend-file should only be required if trying to setup different hugepage configs for each guest NUMA node, or if trying to pin each guest NUMA node to a different host node. If they just want hugepages across the whole VM and no pinning shouldn't the traditional setup work