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

Daniel P. Berrange berrange at redhat.com
Thu Feb 11 14:11:01 UTC 2016

On Thu, Feb 11, 2016 at 01:54:49PM +0300, Pavel Fedin wrote:
>  Hello!
> > Historically QEMU had a pointless check on the path passed in, to enforce
> > that it was only hugetlbfs, so could not just pass in a regular tmpfs
> > file. I think we removed that in QEMU 2.5. I think it is a valid enhance
> > <memoryBacking> to allow specification of "shared" memory backing which
> > would be mapping to a regular tmpfs.
> > 
> > I don't think we should magically do anything based on existance of
> > vhost-user though - changes in way the guest memory is allocated should
> > always require explicit user configuration.
>  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.

>  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.

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