linux-ext4 - Re: [RFC PATCH 2/8] mm: Add PG

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

Message-ID: <87ecq18azq.ritesh.list@gmail.com>
Date: Fri, 14 Nov 2025 10:30:09 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: Matthew Wilcox <willy@...radead.org>, Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc: Christian Brauner <brauner@...nel.org>, djwong@...nel.org, john.g.garry@...cle.com, tytso@....edu, dchinner@...hat.com, hch@....de, linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, jack@...e.cz, nilay@...ux.ibm.com, martin.petersen@...cle.com, rostedt@...dmis.org, axboe@...nel.dk, linux-block@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/8] mm: Add PG_atomic

Matthew Wilcox <willy@...radead.org> writes:

> On Wed, Nov 12, 2025 at 04:36:05PM +0530, Ojaswin Mujoo wrote:
>> From: John Garry <john.g.garry@...cle.com>
>> 
>> Add page flag PG_atomic, meaning that a folio needs to be written back
>> atomically. This will be used by for handling RWF_ATOMIC buffered IO
>> in upcoming patches.
>
> Page flags are a precious resource.  I'm not thrilled about allocating one
> to this rather niche usecase.  Wouldn't this be more aptly a flag on the
> address_space rather than the folio?  ie if we're doing this kind of write
> to a file, aren't most/all of the writes to the file going to be atomic?

As of today the atomic writes functionality works on the per-write
basis (given it's a per-write characteristic). 

So, we can have two types of dirty folios sitting in the page cache of
an inode. Ones which were done using atomic buffered I/O flag
(RWF_ATOMIC) and the other ones which were non-atomic writes. Hence a
need of a folio flag to distinguish between the two writes.

-ritesh