Re: [Xen-devel] [PATCH for-4.5] xen: vnuma: expose vnode_to_pnode to guest

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Nov 10, 2014 at 09:21:24AM +0000, Jan Beulich wrote:
> >>> On 08.11.14 at 20:43, <wei.liu2@xxxxxxxxxx> wrote:
> > This information is passed in in domctl hypercall but the guest
> > interface doesn't expose it to guest. PV NUMA-aware ballooning relies on
> > this piece of information to function properly.
> 
> Considering that exposing this mapping is wrong from a conceptual
> pov (as was discussed during the review of Elena's original series),
> the desire to nevertheless expose it would need to be explained
> much better than what you did above.
> 

My thought was that if a PV guest needs to do NUMA-aware ballooning, it
would be easier to have the mapping at hand to let the guest request
explicitly from what physical node it wants the page. It was based
on my vague memory of early version of Elena's series.

However, if this is conceptually wrong and has been discussed before,
(as I said in the other email) please just ignore this patch. I can try
to modify the hypervisor instead to make NUMA-aware ballooning happen
under the hood without guest knowing anything. That is, to make use of
the vmemrange structure to identify the vnode of a particular gpfn, then
with vnode_to_pnode map to identify the physical node of that gpfn, then
do NUMA-aware ballooning.

Wei.

> Jan

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