[PATCH 00/10] Introduce virtio-mem <memory/> model

[Jing Qi]

Michal,
I checked the virtio_mem module and it's loaded -

lsmod |grep virtio_mem
virtio_mem             32768  0

And I can't make the actual value change to non-zerio.
->  virsh update-memory pc  --requested-size 256M
or
->virsh setmem pc 1000M

 <memory model='virtio-mem'>
      <target>
        <size unit='KiB'>524288</size>
        <node>0</node>
        <block unit='KiB'>2048</block>
        <requested unit='KiB'>262144</requested>
        <actual unit='KiB'>0</actual>
      </target>
      <alias name='virtiomem0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0a'
function='0x0'/>
    </memory>
Any other suggestions ?

> This is a bummer. What this represents is the actual value of membaloon.
> Yes and no. It shows that we need <actual/> because guest might ignore
> request to change the requested size. What you're probably experiencing
> is that you haven't loaded virtio_mem module and thus the virtio-mem
> device is ignoring requests for change (well, kernel is ignoring them,
> whatever).

On Thu, Feb 4, 2021 at 12:27 AM Michal Privoznik <mprivozn at redhat.com>
wrote:

> On 2/3/21 7:11 AM, Jing Qi wrote:
> > I did some test for virtio-mem with libvirt upstream version
> > v7.0.0-153-g5ea3ecd07d
> >   & qemu-kvm-5.2.0-0.7.rc2.fc34.x86_64
> >
> > S1. Start domain with memory device
> >
> > 1. Domain configuration-
> > <maxMemory slots='16' unit='KiB'>10485760</maxMemory>
> >    <memory unit='KiB'>1572864</memory>
> >    <currentMemory unit='KiB'>1572864</currentMemory>
> >   ...
> >    <cpu mode='host-model' check='partial'>
> >      <numa>
> >        <cell id='0' cpus='0-3' memory='1048576' unit='KiB'/>
> >      </numa>
> >    </cpu>
> > ...
> >    <memory model='virtio-mem'>
> >        <target>
> >          <size unit='KiB'>524288</size>
> >          <node>0</node>
> >          <block unit='KiB'>2048</block>
> >          <requested unit='KiB'>393216</requested>
> >        </target>
> >        <address type='pci' domain='0x0000' bus='0x00' slot='0x0a'
> > function='0x0'/>
> >      </memory>
> > #virsh start pc
> >   Domain 'pc'  started
> >
> > 2. The domain is started and check mem status, the actual size is
> "1048576"
> > #virsh dommemstat pc
> > actual 1048576
>
> This is a bummer. What this represents is the actual value of membaloon.
>
> > swap_in 0
> > swap_out 0
> > major_fault 257
> > minor_fault 130540
> > unused 604064
> > available 761328
> > usable 578428
> > last_update 1612325471
> > disk_caches 49632
> > hugetlb_pgalloc 0
> > hugetlb_pgfail 0
> > rss 460260
> >
> > 3. Then, check the active xml -
> > # virsh dumpxml pc
> > ...
> > <memory unit='KiB'>1572864</memory>
> >    <currentMemory unit='KiB'>1048576</currentMemory>
> > ....
> >   <memory model='virtio-mem'>
> >        <target>
> >          <size unit='KiB'>524288</size>
> >          <node>0</node>
> >          <block unit='KiB'>2048</block>
> >          <requested unit='KiB'>393216</requested>
> >          <actual unit='KiB'>0</actual>
> >        </target>
> >        <alias name='virtiomem0'/>
> >        <address type='pci' domain='0x0000' bus='0x00' slot='0x0a'
> > function='0x0'/>
> >      </memory>
> >
> >   Question1 : the value of actual is "0". Is it expected?
>
> Yes and no. It shows that we need <actual/> because guest might ignore
> request to change the requested size. What you're probably experiencing
> is that you haven't loaded virtio_mem module and thus the virtio-mem
> device is ignoring requests for change (well, kernel is ignoring them,
> whatever).
>
> >
> > S2. Also, tried to use hugepage to start the domain -
> >
> > <memory model='virtio-mem'>
> >        <target>
> >          <size unit='KiB'>524288</size>
> >          <node>0</node>
> >          <block unit='KiB'>2048</block>
> >          <requested unit='KiB'>393216</requested>
> >          <actual unit='KiB'>0</actual>
> >        </target>
> >        <alias name='virtiomem0'/>
> >        <address type='pci' domain='0x0000' bus='0x00' slot='0x0a'
> > function='0x0'/>
> >      </memory>
> >
> > #virsh start pc
> > error: Failed to start domain 'pc'
> > error: internal error: process exited while connecting to monitor:
> > 2021-02-03T05:50:33.157836Z qemu-system-x86_64: -object
> >
> memory-backend-file,id=memvirtiomem0,mem-path=/dev/hugepages/libvirt/qemu/9-pc,size=536870912,host-nodes=0,policy=bind:
> > can't open backing store /dev/hugepages/libvirt/qemu/9-pc for guest RAM:
> > Permission denied
> >
> > Question 2: any bug here?
>
> Ah, good catch! I'll fix this in v2.
>
> Michal
>
>

-- 
Thanks & Regards,
Jing,Qi
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