Re: [Qemu-devel] [RFC PATCH v5 6/6] spapr: Don't allow memory hotplug to memory less nodes

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Fri, Jun 26, 2015 at 03:33:29PM +1000, David Gibson wrote:
> On Thu, Jun 25, 2015 at 11:44:15AM +0530, Bharata B Rao wrote:
> > Currently PowerPC kernel doesn't allow hot-adding memory to memory-less
> > node, but instead will silently add the memory to the first node that has
> > some memory. This causes two unexpected behaviours for the user.
> > 
> > Memory gets hotplugged to a different node than what the user specified.
> > Since pc-dimm subsystem in QEMU still thinks that memory belongs to
> > memory-less node, a reboot will set things accordingly and the previously
> > hotplugged memory now ends in the right node. This appears as if some
> > memory moved from one node to another.
> > 
> > So until kernel starts supporting memory hotplug to memory-less
> > nodes, just prevent such attempts upfront in QEMU.
> > 
> > Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> 
> I presume you're talking about host kernel limitations here?

No, this is a guest kernel limitation. Pls refer to the related discussions
about this here:

https://lkml.org/lkml/2015/6/24/1

> 
> If that does get changed in future we'll need some sort of ugly compat
> test in qemu to see if the new kernel can handle it, but there's no
> way to avoid that, so.

Yeah, I see that.

Regards,
Bharata.