linux-kernel - Re: [PATCH v9 13/15] xfs: add xfs_compute_atomic_write_unit

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Message-ID: <01f9a1df-859b-4117-8e12-cb06edee9f17@oracle.com>
Date: Thu, 1 May 2025 06:00:12 +0100
From: John Garry <john.g.garry@...cle.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: brauner@...nel.org, hch@....de, 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 v9 13/15] xfs: add xfs_compute_atomic_write_unit_max()

On 01/05/2025 05:30, Darrick J. Wong wrote:
> On Wed, Apr 30, 2025 at 08:52:00AM +0100, John Garry wrote:
>> On 25/04/2025 17:45, John Garry wrote:
>>> +static inline xfs_extlen_t xfs_calc_perag_awu_max(struct xfs_mount *mp)
>>> +{
>>> +	if (mp->m_ddev_targp->bt_bdev_awu_min > 0)
>>> +		return max_pow_of_two_factor(mp->m_sb.sb_agblocks);
>>> +	return mp->m_ag_max_usable;
>> I think that this should be rounddown_pow_of_two(mp->m_ag_max_usable)
>>
>> ditto for rt
>>
>> I will fix (unless disagree).
> I don't think this needs fixing.  If there's no hardware support on the
> device, then we can do any size of atomic write that we want.

Check man pages for statx:

stx_atomic_write_unit_min
stx_atomic_write_unit_max
               ... These values are each guaranteed to be
               a power-of-2.

Same is enforced for size for RWF_ATOMIC.