Re: [Qemu-devel] [PATCH v2] balloon: Fix failure of updating guest memory status

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jul 06, 2016 at 09:23:46AM +0000, Li, Liang Z wrote:
> > On Wed, Jul 06, 2016 at 10:36:33AM +0800, Liang Li wrote:
> > > After live migration, 'guest-stats' can't get the expected memory
> > > status in the guest. This issue is caused by commit 4eae2a657d.
> > > The value of 's->stats_vq_elem' will be NULL after live migration, and
> > > the check in the function 'balloon_stats_poll_cb()' will prevent the
> > > 'virtio_notify()' from executing. So guest will not update the memory
> > > status.
> > >
> > > Commit 4eae2a657d is doing the right thing, but 's->stats_vq_elem'
> > > should be treated as part of balloon device state and migrated to
> > > destination if it's not NULL to make everything works well.
> > >
> > > Signed-off-by: Liang Li <liang.z.li@intel.com>
> > > Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> > > Cc: Michael S. Tsirkin <mst@redhat.com>
> > > Cc: Ladi Prosek <lprosek@redhat.com>
> > > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > 
> > I agree there's an issue but we don't change versions anymore.
> > Breaking migrations for everyone is also not nice.
> > 
> > How about queueing virtio_balloon_receive_stats so it will get invoked when
> > vm starts?
> > 
> 
> Could you give more explanation about how it works?  I can't catch you.
> 
> Thanks!
> Liang

virtqueue_discard before migration

virtio_balloon_receive_stats after migration

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MST