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

[Christoph Hellwig]

On Tue, Jan 29, 2019 at 01:43:02PM -0700, Logan Gunthorpe wrote:
> It's hard to reason about an interface when you can't see what all the
> layers want to do with it. Most maintainers (I'd hope) would certainly
> never merge code that has no callers, and for much the same reason, I'd
> rather not review patches that don't have real use case examples.

Yes, we should never review, nevermind merge code without users.
We had one example recently where this was not followed, which was HMM
and that turned out to be a desaster.