Re: [PATCH 1/4] mm: Trial do_wp_page() simplification

Linus Torvalds
2022-02-16T19:12:21Z

[ Added David Hildenbrand to the participants. David, see

https://bugzilla.kernel.org/show_bug.cgi?id=215616

for details ]

On Wed, Feb 16, 2022 at 8:59 AM Oded Gabbay <oded.gabbay@gmail.com> wrote:
>
> All the details are in the bug, but the bottom line is that somehow,
> this patch causes corruption when the numa balancing feature is
> enabled AND we don't use process affinity AND we use GUP to pin pages
> so our accelerator can DMA to/from system memory.

Hmm. I thought all the remaining issues were related to THP - and
David Hildenbrand had a series to fix those up.

The fact that it also shows up with numa balancing is a bit
unfortunate, because I think that means that that patch series may not
have caught that case.

That said - what does "we use GUP to pin pages" mean? Does it actually
use the pinning logic, or just regular old GUP?

I'm assuming this is just the existing pin_user_pages_fast() (ie a
proper pin) in drivers/misc/habanalabs/common/memory.c. But I wanted
to confirm that it's not some other situation.

Linus