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

From: Jason Gunthorpe
Date: Mon Feb 11 2019 - 15:40:58 EST

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?