Re: [PATCH 0/3] Add gup fast + longterm and use it in HFI1

[Jason Gunthorpe]

On Mon, Feb 11, 2019 at 12:16:40PM -0800, ira.weiny@xxxxxxxxx wrote:
> From: Ira Weiny <ira.weiny@xxxxxxxxx>
> 
> NOTE: This series depends on my clean up patch to remove the write parameter
> from gup_fast_permitted()[1]
> 
> HFI1 uses get_user_pages_fast() due to it performance advantages.  Like RDMA,
> HFI1 pages can be held for a significant time.  But get_user_pages_fast() does
> not protect against mapping of FS DAX pages.

If HFI1 can use the _fast varient, can't all the general RDMA stuff
use it too? 

What is the guidance on when fast vs not fast should be use?

Jason