linux-kernel - Re: [PATCH v8 05/15] xfs: ignore HW which cannot atomic write a single block

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Message-ID: <20250423151224.GC25675@frogsfrogsfrogs>
Date: Wed, 23 Apr 2025 08:12:24 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: John Garry <john.g.garry@...cle.com>, brauner@...nel.org,
	viro@...iv.linux.org.uk, jack@...e.cz, cem@...nel.org,
	linux-fsdevel@...r.kernel.org, dchinner@...hat.com,
	linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	ojaswin@...ux.ibm.com, ritesh.list@...il.com,
	martin.petersen@...cle.com, linux-ext4@...r.kernel.org,
	linux-block@...r.kernel.org, catherine.hoang@...cle.com,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v8 05/15] xfs: ignore HW which cannot atomic write a
 single block

On Wed, Apr 23, 2025 at 10:33:17AM +0200, Christoph Hellwig wrote:
> On Wed, Apr 23, 2025 at 09:28:14AM +0100, John Garry wrote:
> >> But maybe we should just delay setting the atomic values until later so
> >> that it can be done in a single pass?  E.g. into xfs_setsize_buftarg
> >> which then should probably be rename to something like
> >> xfs_buftarg_setup.
> >>
> >
> > How about just do away with btp->bt_bdev_awu_{min, max} struct members, and 
> > call bdev_atomic_write_unit_max(mp->m_ddev_targp->bt_bdev) [and same for 
> > RT] to later to set the mp awu max values at mountfs time? I think that 
> > would work..
> 
> Sounds reasonable.

I disagree, leaving the hardware awu_min/max in the buftarg makes more
sense to me because the buftarg is our abstraction for a block device,
and these fields describe the atomic write units that we can use with
that block device.

IOWs, I don't like dumping even more into struct xfs_mount.  xfs_group
has an awu_max for the software fallback, xfs_buftarg has an awu_min/max
for hardware, and even this V8 has yet a third pair of awu_min/max in
xfs_mount which I think is just the buftarg version but possibly
truncated.  I find those last two pairs confusing.

--D