Re: [PATCH v1 00/16] NFS/RDMA patches proposed for 4.1

[Christoph Hellwig <hch@infradead.org>]

On Tue, May 05, 2015 at 02:14:30PM -0400, Tom Talpey wrote:
> As you might guess, I can go on at length about this. :-) But, if
> you have a kernel service, the ability to pin memory, and you
> want it to go fast, you want FRWR.

Basically most in-kernel consumers seem to have the same requirements:

 - register a struct page, which can be kernel or user memory (it's
   probably pinned in your Terms, but we don't really use that much in
   kernelspace).
 - In many but not all cases we might need an offset/length for each
   page (think struct bvec, paged sk_buffs, or scatterlists of some
   sort), in other an offset/len for the whole set of pages is fine,
   but that's a superset of the one above.
 - we usually want it to be as fast as possible

While my grep skills aren't the best I can't really find an in-kernel
user that doesn't fit the above, although I might have missed some
long-term registrations where we don't really care about the fast
part.