linux-kernel - Re: [PATCH 0/2] fs/proc: extend the PAGEMAP

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Message-ID: <24d6f7a9-82db-4240-a8d6-2c8b58861521@lucifer.local>
Date: Thu, 20 Mar 2025 10:57:45 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrei Vagin <avagin@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-doc@...r.kernel.org, David Hildenbrand <david@...hat.com>,
        Shuah Khan <shuah@...nel.org>, Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH 0/2] fs/proc: extend the PAGEMAP_SCAN ioctl to report

Well I guess it couldn't wait ;) we're (very!) late in the cycle and
immediately pre-LSF (will you be there btw?) so this is 6.16 for sure.

Kinda wish you'd mentioned you wanted to do it as I'd rearranged my
schedule to tackle this as a priority post-LSF, but you've done a good job
so we're all good! Just a little heads up would have been nice ;)

Some nits and you need to fix the test header thing but otherwise good.

On Thu, Mar 20, 2025 at 06:39:01AM +0000, Andrei Vagin wrote:
> Introduce the PAGE_IS_GUARD flag in the PAGEMAP_SCAN ioctl to expose
> information about guard regions. This allows userspace tools, such as
> CRIU, to detect and handle guard regions.

Might be worth underlining why it is so crucial for CRIU, and what
advantages PAGEMAP_SCAN confers.

>
> This series should be applied on top of "[PATCH 0/2] fs/proc/task_mmu:
> add guard region bit to pagemap":
> https://lore.kernel.org/all/2025031926-engraved-footer-3e9b@gregkh/T/

No need for this, this applies fine against mm-unstable, though we're
looking at 6.16 for this now obviously.

>
> The series includes updates to the documentation and selftests to
> reflect the new functionality.

I love to see it! :>)

Please also, once this moves along, send an update to the manpage please.

>
> Andrei Vagin (2):
>   fs/proc: extend the PAGEMAP_SCAN ioctl to report guard regions
>   selftests/mm: add PAGEMAP_SCAN guard region test
>
>  Documentation/admin-guide/mm/pagemap.rst   |  1 +
>  fs/proc/task_mmu.c                         |  8 +++-
>  include/uapi/linux/fs.h                    |  1 +
>  tools/testing/selftests/mm/guard-regions.c | 53 ++++++++++++++++++++++
>  4 files changed, 61 insertions(+), 2 deletions(-)
>
> --
> 2.49.0.rc1.451.g8f38331e32-goog
>

Cheers, Lorenzo