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

On Mon, Feb 11, 2019 at 12:16:40PM -0800, ira.weiny@intel.com wrote:

From: Ira Weiny <redacted>

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