libvirt users - Sep 2014 - Re: what is the xml fomat about memory-backend-file

Hi,

I want to use virsh to create a VM with the qemu parameter '-object
memory-backend-file,id=mem,size=2048M,mem-path=/mnt/huge,share=on -numa
node,memdev=mem'.

How to write the XML file?

On 09/24/2014 02:05 AM, Linhaifeng wrote:
> Hi,
> 
> I want to use virsh to create a VM with the qemu parameter '-object
memory-backend-file,id=mem,size=2048M,mem-path=/mnt/huge,share=on -numa
node,memdev=mem'.
Looking at tests/qemuxml2argvdata/qemuxml2argv-hugepages-pages.args, I
see several instances of "-object memory-backend-file...", so look at
the counterpart .xml file for some examples:

  <memoryBacking>
    <hugepages>
      <page size='2048' unit='KiB' nodeset='1'/>
      <page size='1048576' unit='KiB'
nodeset='0,2-3'/>
    </hugepages>
  </memoryBacking>


-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

On 2014/9/25 2:05, Eric Blake wrote:
> On 09/24/2014 02:05 AM, Linhaifeng wrote:
>> Hi,
>>
>> I want to use virsh to create a VM with the qemu parameter '-object
memory-backend-file,id=mem,size=2048M,mem-path=/mnt/huge,share=on -numa
node,memdev=mem'.
> 
> Looking at tests/qemuxml2argvdata/qemuxml2argv-hugepages-pages.args, I
> see several instances of "-object memory-backend-file...", so
look at
> the counterpart .xml file for some examples:
> 
>   <memoryBacking>
>     <hugepages>
>       <page size='2048' unit='KiB'
nodeset='1'/>
>       <page size='1048576' unit='KiB'
nodeset='0,2-3'/>
>     </hugepages>
>   </memoryBacking>
> 
> 
Thank you.

I use this xml:
  <cpu>
    <numa>
      <cell id='0' cpus='0' memory='1073741824'
memAccess='shared'/>
      <cell id='1' cpus='1' memory='1073741824'
memAccess='shared'/>
    </numa>
  </cpu>
 <memoryBacking>
    <hugepages>
      <page size="2" unit="M"
nodeset="0,1"/>
    </hugepages>
 </memoryBacking>

but there is also some error:
[2014-09-28T05:28:32.373335Z] migration_configure:652 Parameter 'cache
size' expects exceeds guest ram size
[2014-09-28T05:28:32.373422Z] main:3517 start memory options parse
2014-09-28T05:28:32.373802Z qemu-kvm: -object
memory-backend-file,prealloc=yes,mem-path=/dev/hugepages/libvirt/qemu,size=1048576M,id=ram-node0:
unable to map backing store for hugepages: Cannot allocate memory
2014-09-28T05:28:32.373895Z qemu-kvm: -object
memory-backend-file,prealloc=yes,mem-path=/dev/hugepages/libvirt/qemu,size=1048576M,id=ram-node1:
unable to map backing store for hugepages: Cannot allocate memory