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

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Message-ID: <aRSuH82gM-8BzPCU@casper.infradead.org>
Date: Wed, 12 Nov 2025 15:56:15 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc: Christian Brauner <brauner@...nel.org>, djwong@...nel.org,
	ritesh.list@...il.com, 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

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?