Re: [Qemu-devel] [PATCH v2 1/3] pc-dimm: add a function to calculate VM's current RAM size

[Michael S. Tsirkin]

On Wed, Nov 19, 2014 at 09:31:35AM -0700, Eric Blake wrote:
> On 11/19/2014 09:06 AM, Michael S. Tsirkin wrote:
> 
> >>>> This affects QMP right?
> >>>
> >>> I think later patches will tell how. CC'ing Eric.
> >>
> >> As far as I can tell, this is just correcting a reporting issue; the
> >> existing QMP commands/events for tracking balloon size will now properly
> >> account for hotplugged memory.
> >>
> >> What I don't know is if this change in semantics will affect any users.
> >>  Libvirt is not yet supporting memory hotplug, so ideally, fixing this
> >> bug before libvirt uses memory hotplug means libvirt will never have to
> >> worry about qemu versions that do incorrect reporting.
> >>
> >> The alternative is to declare that the existing QMP commands cannot
> >> change in semantics for the existing members that it reports, and must
> >> instead report additional dictionary members describing the amount of
> >> hot-plugged memory, and then require that the client add the numbers
> >> together itself.  That sounds mean to the client, so I'm hoping we don't
> >> have to go there.
> > 
> > 
> > IOW you ack this patch for 2.2?
> > 
> 
> Is memory hotplug one of the new features in 2.2?  If so, then yes, we
> should get its semantics right from the start (this is a bug fix to
> avoid a release with broken semantics).  On the other hand, if hotplug
> existed in 2.1, then we already have a release with odd semantics, so
> delaying this fix until 2.3 and leaving 2.2 with the same odd semantics
> would not hurt, and it then becomes a judgment call of whether we are
> rushing in a possibly incomplete solution by trying to get this into
> 2.2. (Sorry I haven't been following the history of memory hotplug closer)

AFAIK it's there since 2.0.


> 
> -- 
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>