turn the hmm migrate_vma upside down

[Jason Gunthorpe]

On Mon, Jul 29, 2019 at 05:28:34PM +0300, Christoph Hellwig wrote:
> Hi Jérôme, Ben and Jason,
> 
> below is a series against the hmm tree which starts revamping the
> migrate_vma functionality.  The prime idea is to export three slightly
> lower level functions and thus avoid the need for migrate_vma_ops
> callbacks.

I don't feel I can contribute a worthwhile review for this part of the
code right now.

Does this only impact hmm users, or does migrate.c have a broader
usage?

Who do we need on review to progress on this?

Thanks,
Jason