Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device vma

[Jason Gunthorpe]

On Tue, Jan 29, 2019 at 01:39:49PM -0700, Logan Gunthorpe wrote:

> implement the mapping. And I don't think we should have 'special' vma's
> for this (though we may need something to ensure we don't get mapping
> requests mixed with different types of pages...).

I think Jerome explained the point here is to have a 'special vma'
rather than a 'special struct page' as, really, we don't need a
struct page at all to make this work.

If I recall your earlier attempts at adding struct page for BAR
memory, it ran aground on issues related to O_DIRECT/sgls, etc, etc.

This does seem to avoid that pitfall entirely as we can never
accidently get into the SGL system with this kind of memory or VMA?

Jason