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

[Dario Faggioli <dario.faggioli@citrix.com>]

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On Mon, 2014-11-10 at 11:27 +0000, Wei Liu wrote:
> On Mon, Nov 10, 2014 at 11:21:40AM +0000, David Vrabel wrote:
> > On 10/11/14 11:09, Wei Liu wrote:
> > > 
> > > 3. Don't expose anything, everything happens automagically without guest
> > >    knowing anything.
> > 
> > This.  The vnode to pnode mapping can change on a save/restore.
> 
> I don't think this is the most decisive reasoning of this issue. The
> other two options can also deal with this -- just retrieve the
> up-to-date versions after migration.
> 
IMO, what's needed is an "on demand" "translation service". The guest
should not store the result of such translation and rely on it.

The opposite, actually: when ballooning up (i.e., the only legittimate
use case of this "service" I can think of right now), it should be
possible to let the hypervisor know from what physical NUMA node we want
a page, basing on which vnode such page belongs to.

This is probably another argument for not using option 1, and for going
for 3, if possible, or with something different, if not.

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)


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