----- Original Message -----
> From: "Dan Kenigsberg" <dan...@redhat.com>
> To: "Gal Hammer" <gham...@redhat.com>
> Cc: email@example.com
> Sent: Sunday, April 29, 2012 7:19:10 AM
> Subject: Re: [vdsm] reserve virtio-balloon device created by libvirt
> On Mon, Apr 23, 2012 at 04:00:55PM +0300, Gal Hammer wrote:
> > On 23/04/2012 12:26, Mark Wu wrote:
> > >Hi guys,
> > >
> > >I saw that an option to create balloon device was added by Gal in
> > >http://gerrit.ovirt.org/1573
> > >I have a question about it. Why don we preserve the old default
> > >behaviour? I know it's not supported by ovirt-engine now, but I
> > >can't
> > >figure out what will break if it's not disabled explicitly. So do
> > >you
> > >think we can just make use of the balloon device added by libvirt?
> > We didn't change the old behavior.
> > Libvirt creates by default a memory-balloon device, so vdsm
> > defaults
> > was to disable it by adding a "none"-type device. This was done
> > because vdsm didn't include an option to add such device.
> > My patch added an option to create a memory-balloon through vdsm.
> > If
> > the user didn't request to add the device, the behavior is same as
> > before, disabling the memory-balloon.
> I feel that it would be best not to flip Vdsm's default at the
> even though it is the opposite of libvirt's. I would consider to flip
> them only after your (Mark's) patches are in, tested, and proven
> worthwhile for the common case.
> Currently, without any management for the balloon, reserving a guest
> device was deemed wasteful.
On the other side of the fence
- We know that we do need to do ballooning
- In the (next?) release we'll end up adding this support
- There's no harm (see next point) in adding the device now in fact it saves a
config change on upgrade.
- While it takes up a PCI slot it's going to be very, very rare deployments
that will ever see the limit, libvirt/virtmanager/virt-install has done this
forever without seeing push back.
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