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
