[libvirt] [RFC] vhost-user + shared memory + NUMA

[Pavel Fedin]

 Hello!

> >  Ok, then would it be a good compromise if we require <memoryBacking>, and only implicitly
> add "shared" if we have vhost-user
> > devices? This way we would not change the way the guest memory is allocated.
> 
> Adding shared implicitly *will* change the way guest memory is allocated,
> as it will have to use tmpfs to make it shared.

 You perhaps didn't get my idea. I meant - we will still need to specify <memoryBacking> with huge pages, just no <numa>. Therefore, the memory will be allocated via file backend from hugetlbfs. Only mode will be changed implicitly (private -> shared).

> >  IMHO being able to manually specify "shared" both in <numa> and
> > in <memoryBacking> would be ambiguous.
> 
> That's not really any different to what we have already with NUMA.
> The top level setting would apply as the default, and the NUMA level
> settings override it if needed.

 Well, the only little drawback would be necessity to add "shared" by itself. This would require additional patching to clients (e. g. openstack).

Kind regards,
Pavel Fedin
Senior Engineer
Samsung Electronics Research center Russia