[PATCH 0 of 2 RFC] xl: move domeins among NUMA nodes

[Dario Faggioli <raistlin@linux.it>]

Hello Everyone,

FIRST OF ALL, this is an RFC and, more important, it implements a new feature
(although it's a small one), so it is not meant for 4.2. Of course, comments
are more than welcome, if you happen to find the time to look at it (after all,
it is why I'm releasing it)... Just don't rush if you're busy with some
pressing release-related stuff! :-P

The above being stated, this series tries to tackle the problem of moving an
already existent domain from a (some) NUMA node(s) to a (some) other(s). In
fact, changing vcpu-affinity affects the node affinity of the domain itself,
but this is only effective wrt the memory that will be allocated in the future,
while all the existent pages are untouched. This of course makes a lot of
sense, but there might be the need to _fully_ move a domain, both vcpus and
memory wise, and that's what this series tries to achieve.

Just let me add that the whole process looks a lot like a suspend/resume (or
either to a local migration) to me, and that's why I implemented it like that
for now. I went for the suspend resume approach, but I think I can make it more
migration-oriented solution if wanted, as it'd reduce the downtime (although,
in that case, we'd need to have twice the memory of the domain available during
the process).
Of course, I can also add the proper logic and interface to the hypervisor, but
I'm not sure it buys that much, as there will still be something very similar
to suspension or migration, just called and used a little bit differently (but
of course I'm open to change my mind :-)).

Thanks and Regards,
Dario

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