[libvirt-users] what is the xml fomat about memory-backend-file

[Linhaifeng]

On 2014/9/28 16:19, Jincheng Miao wrote:
> 
> On 09/28/2014 01:38 PM, Linhaifeng wrote:
>>
>> 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
> 
> get total number of the hugepages you could use:
> # cat /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> 
> From your xml:
>       <cell id='0' cpus='0' memory='1073741824' memAccess='shared'/>
>       <cell id='1' cpus='1' memory='1073741824' memAccess='shared'/>
> I guess your machine doesn't have so much hugepage memory: sum(1073741824 + 1073741824)=2048G !!!
> 

Thank you.
Yes,you are right.This is my mistake.Actually i want to use 1G.


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