Re: [Qemu-devel] ballooning not working on hotplugged pc-dimm

[Michael R. Hines]

On 09/10/2014 05:00 PM, zhanghailiang wrote:
> On 2014/9/9 11:05, Alexandre DERUMIER wrote:
> > Hello,
> >
> > I was playing with pc-dimm hotplug, and I notice that balloning is 
> > not working on
> > memory space of pc-dimm devices.
> >
> > example:
> >
> > qemu -m size=1024,slots=255,maxmem=15000M
> >
> > #free -m : 1024M
> > ->  qmp balloon 512M
> > #free -m : 512M
> >
> > ->  hotplug pc-dimm 1G:
> >
> > #free -m : 1512M
> >
> >
> > (This is the same behavior if qemu is started with pc-dimm devices)
> >
> >
> > qemu 2.1
> > Guest kernel : 3.12.
> >
> >
> >
> > Does it need a guest balloon module update ?
> >
> > Regards,
> >
> > Alexandre Derumier
> Hi,
>
> I noticed this fault also;-), this is a bug in qemu, And some work in 
> process...
>
> Actually in QEMU the hotplugged memory(named hotplug-memory) is 
> distinguished
> from the common memory(named pc.ram). When do balloon action, QEMU 
> wrongly
> stats the ram_size.
>
> I will send a patch series which also include other bug fix for the 
> memory hotplug.
>
> Thanks,
> zhanghailiang

Why does hotplugging use a different name?

This also affects RDMA live migration - we are explicitly looking up 
"pc.ram" ram blocks and pinning them for memory registration with Linux.

- Michael