linux-kernel - Re: [PATCH v3 3/3] xfs: reject max_atomic

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Message-ID: <20250725154950.GQ2672029@frogsfrogsfrogs>
Date: Fri, 25 Jul 2025 08:49:50 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: John Garry <john.g.garry@...cle.com>
Cc: hch@....de, cem@...nel.org, dan.j.williams@...el.com,
	willy@...radead.org, jack@...e.cz, brauner@...nel.org,
	viro@...iv.linux.org.uk, linux-xfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, nvdimm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/3] xfs: reject max_atomic_write mount option for no
 reflink

On Fri, Jul 25, 2025 at 09:39:42AM +0100, John Garry wrote:
> On 24/07/2025 17:32, Darrick J. Wong wrote:
> > On Thu, Jul 24, 2025 at 08:12:15AM +0000, John Garry wrote:
> > > If the FS has no reflink, then atomic writes greater than 1x block are not
> > > supported. As such, for no reflink it is pointless to accept setting
> > > max_atomic_write when it cannot be supported, so reject max_atomic_write
> > > mount option in this case.
> > > 
> > > It could be still possible to accept max_atomic_write option of size 1x
> > > block if HW atomics are supported, so check for this specifically.
> > > 
> > > Fixes: 4528b9052731 ("xfs: allow sysadmins to specify a maximum atomic write limit at mount time")
> > > Signed-off-by: John Garry<john.g.garry@...cle.com>
> > /me wonders if "mkfs: allow users to configure the desired maximum
> > atomic write size" needs a similar filter?
> > 
> 
> Yeah, probably. But I am wondering if we should always require reflink for
> setting that max atomic mkfs option, and not have a special case of HW
> atomics available for 1x blocksize atomic writes.

I think that's reasonable for mkfs since reflink=1 has been the default
for quite a long while now.

--D

> > Reviewed-by: "Darrick J. Wong"<djwong@...nel.org>
> 
> cheers
>