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

[zhanghailiang]

On 2014/11/20 0:31, 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

No, after searching this feature in ChangeLogs, i found pc-dimm memory hotplug
was supported since 2.1. It only supports for x86 target.

And one more thing, i found in 2.2's Changelog it begin to support memory 
hotplug
for s390 target, I'm not sure whether this problem also exists for s390.

> 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)