[libvirt-users] Incorrect currentMemory for qemu-1.2+

[Andrey Korolyov]

Hi,

Since this message(https://www.redhat.com/archives/libvirt-users/2012-October/msg00054.html)
qemu folks have released one minor version in the 1.2 branch and shiny
new 1.3 some days ago and the problem still persists. At first I has
blamed libvirt, but I was not correct at all - since I have released
package ``slices'' for myself including both newer libvirth and qemu,
I wasn`t able to corner this problem and my report may be counted as
completely wrong.

Right now, I have the following situation:

- all libvirt versions running above qemu-1.1 always reports right
balloon and currentMemory sizes

- for qemu 1.2 it is quite more funny: as in message above, I receive
wrong currentMemory always set to ``magic'' 5398528kB at the 8gb host
node, but only if ``memory'' parameter has same or higher value, even
<memory unit='KiB'>5348520</memory> works okay, providing righ balloon
value for the libvirt. As you can see the ~2700MB offset between
current and maximum(or entire host) memory present in both
configurations. 8Gb node is a simple non-numa machine so this is not
related to numa miscalculation. Previous test at the link above
processed on the 64GB two-head node with symmetric numa topology, if
it matters.

And finally,

$ virsh dumpxml vm010-000-000-092 | grep curr
  <currentMemory unit='KiB'>5398528</currentMemory>
$ virsh qemu-monitor-command --hmp vm010-000-000-092 info balloon
balloon: actual=1176

Until virtio_balloon initializes in the guest, libvirt reporting
_right_ value for some seconds after VM start, so bug (which I unable
to track by myself) almost for sure presented in parsing of received
values from guest balloon.