Re: [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM

[Jason Gunthorpe]

On Sun, Oct 04, 2020 at 01:20:31PM +0200, Daniel Vetter wrote:

> Yeah I think that works. I tried understanding gup.c code a bit more,
> and it looks like FOLL_LONGTERM only works for the pup_fast variant
> right now? All others seem to have this comment that it's somehow
> incompatible with FAULT_FLAG_ALLOW_RETRY and daxfs. But grepping
> around for that didn't show up anything, at least not nearby dax code.
> For my understanding of all this, what's the hiccup there?

IIRC it needs the VMA and various other flows can't return the vma
list becuse they unlock the mmap_sem will running

> For plans, I only started this for a bit of my own learning, but I
> think I'll respin with the following changes:
> - convert exynos and habanalabs to pin_user_pages_fast directly,
> instead of going through this frame-vector detour

+1

Jason