linux-kernel - Re: [PATCH 1/4] mm: Trial do_wp

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Date:   Wed, 16 Feb 2022 11:04:28 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Oded Gabbay <oded.gabbay@...il.com>,
        David Hildenbrand <david@...hat.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, Jan Kara <jack@...e.cz>,
        John Hubbard <jhubbard@...dia.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Maya B . Gokhale" <gokhale2@...l.gov>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Marty Mcfadden <mcfadden8@...l.gov>,
        Kirill Shutemov <kirill@...temov.name>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification

[ 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@...il.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