revamp vmem_altmap / dev_pagemap handling V3

[Jerome Glisse]

On Mon, Jan 08, 2018 at 12:26:46PM +0100, Christoph Hellwig wrote:
> Any chance to get this fully reviewed and picked up before the
> end of the merge window?

Sorry for taking so long to get to that, i looked at all the patches
and did not see anything obviously wrong and i like the cleanup so

Reviewed-by: Jérôme Glisse <jglisse at redhat.com>