linux-kernel - Re: [PATCH v2] mm: skip folio_activate() for mlocked folios

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAKEwX=O2CMnufzuU7n32BD+SD5Oapmct=YGUUQFZ=2w+u2kGvA@mail.gmail.com>
Date: Tue, 7 Oct 2025 09:26:59 -0700
From: Nhat Pham <nphamcs@...il.com>
To: Dmitry Ilvokhin <d@...okhin.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Kemeng Shi <shikemeng@...weicloud.com>, 
	Kairui Song <kasong@...cent.com>, Baoquan He <bhe@...hat.com>, Barry Song <baohua@...nel.org>, 
	Chris Li <chrisl@...nel.org>, Axel Rasmussen <axelrasmussen@...gle.com>, 
	Yuanchu Xie <yuanchu@...gle.com>, Wei Xu <weixugc@...gle.com>, 
	Kiryl Shutsemau <kas@...nel.org>, Usama Arif <usamaarif642@...il.com>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH v2] mm: skip folio_activate() for mlocked folios

On Mon, Oct 6, 2025 at 6:25 AM Dmitry Ilvokhin <d@...okhin.com> wrote:
>
> __mlock_folio() does not move folio to unevicable LRU, when
> folio_activate() removes folio from LRU.
>
> To prevent this case also check for folio_test_mlocked() in
> folio_mark_accessed(). If folio is not yet marked as unevictable, but
> already marked as mlocked, then skip folio_activate() call to allow
> __mlock_folio() to make all necessary updates. It should be safe to skip
> folio_activate() here, because mlocked folio should end up in
> unevictable LRU eventually anyway.
>
> To observe the problem mmap() and mlock() big file and check Unevictable
> and Mlocked values from /proc/meminfo. On freshly booted system without
> any other mlocked memory we expect them to match or be quite close.
>
> See below for more detailed reproduction steps. Source code of stat.c is
> available at [1].
>
>   $ head -c 8G < /dev/urandom > /tmp/random.bin
>
>   $ cc -pedantic -Wall -std=c99 stat.c -O3 -o /tmp/stat
>   $ /tmp/stat
>   Unevictable:     8389668 kB
>   Mlocked:         8389700 kB
>
>   Need to run binary twice. Problem does not reproduce on the first run,
>   but always reproduces on the second run.
>
>   $ /tmp/stat
>   Unevictable:     5374676 kB
>   Mlocked:         8389332 kB
>
> [1]: https://gist.github.com/ilvokhin/e50c3d2ff5d9f70dcbb378c6695386dd
>
> Co-developed-by: Kiryl Shutsemau <kas@...nel.org>
> Signed-off-by: Kiryl Shutsemau <kas@...nel.org>
> Signed-off-by: Dmitry Ilvokhin <d@...okhin.com>
> Acked-by: Usama Arif <usamaarif642@...il.com>

Acked-by: Nhat Pham <nphamcs@...il.com>