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. IMHO being able to manually specify "shared" both in <numa> and in <memoryBacking> would be ambiguous. Kind regards, Pavel Fedin Senior Engineer Samsung Electronics Research center Russia