linux-kernel - Re: [PATCH v2] mm: fault in complete folios instead of individual pages for tmpfs

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: <DDA700FC-6FB3-41BD-A409-AA82A94DE406@nvidia.com>
Date: Fri, 04 Jul 2025 18:31:04 -0400
From: Zi Yan <ziy@...dia.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.com, david@...hat.com,
 lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, npache@...hat.com,
 ryan.roberts@....com, dev.jain@....com, baohua@...nel.org, vbabka@...e.cz,
 rppt@...nel.org, surenb@...gle.com, mhocko@...e.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: fault in complete folios instead of individual
 pages for tmpfs

On 3 Jul 2025, at 23:19, Baolin Wang wrote:

> After commit acd7ccb284b8 ("mm: shmem: add large folio support for tmpfs"),
> tmpfs can also support large folio allocation (not just PMD-sized large
> folios).
>
> However, when accessing tmpfs via mmap(), although tmpfs supports large folios,
> we still establish mappings at the base page granularity, which is unreasonable.
>
> We can map multiple consecutive pages of a tmpfs folios at once according to
> the size of the large folio. On one hand, this can reduce the overhead of page
> faults; on the other hand, it can leverage hardware architecture optimizations
> to reduce TLB misses, such as contiguous PTEs on the ARM architecture.
>
> Moreover, tmpfs mount will use the 'huge=' option to control large folio
> allocation explicitly. So it can be understood that the process's RSS statistics
> might increase, and I think this will not cause any obvious effects for users.
>
> Performance test:
> I created a 1G tmpfs file, populated with 64K large folios, and write-accessed it
> sequentially via mmap(). I observed a significant performance improvement:
>
> Before the patch:
> real	0m0.158s
> user	0m0.008s
> sys	0m0.150s
>
> After the patch:
> real	0m0.021s
> user	0m0.004s
> sys	0m0.017s
>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
> Changes from v1:
>  - Drop the unnecessary IS_ALIGNED() check, per David.
>  - Update the commit message, per David.
> ---
>  mm/memory.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>

LGTM. Acked-by: Zi Yan <ziy@...dia.com>


--
Best Regards,
Yan, Zi