linux-kernel - Re: [PATCH v3 09/21] xfs: Do not free EOF blocks for forcealign

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Date: Wed, 1 May 2024 08:54:06 +1000
From: Dave Chinner <david@...morbit.com>
To: John Garry <john.g.garry@...cle.com>
Cc: djwong@...nel.org, hch@....de, viro@...iv.linux.org.uk,
	brauner@...nel.org, jack@...e.cz, chandan.babu@...cle.com,
	willy@...radead.org, axboe@...nel.dk, martin.petersen@...cle.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	tytso@....edu, jbongio@...gle.com, ojaswin@...ux.ibm.com,
	ritesh.list@...il.com, mcgrof@...nel.org, p.raghav@...sung.com,
	linux-xfs@...r.kernel.org, catherine.hoang@...cle.com
Subject: Re: [PATCH v3 09/21] xfs: Do not free EOF blocks for forcealign

On Mon, Apr 29, 2024 at 05:47:34PM +0000, John Garry wrote:
> For when forcealign is enabled, we want the EOF to be aligned as well, so
> do not free EOF blocks.

This is doesn't match what the code does. The code is correct - it
rounds the range to be trimmed up to the aligned offset beyond EOF
and then frees them. The description needs to be updated to reflect
this.

> 
> Signed-off-by: John Garry <john.g.garry@...cle.com>
> ---
>  fs/xfs/xfs_bmap_util.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index 19e11d1da660..f26d1570b9bd 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -542,8 +542,13 @@ xfs_can_free_eofblocks(
>  	 * forever.
>  	 */
>  	end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)XFS_ISIZE(ip));
> -	if (XFS_IS_REALTIME_INODE(ip) && mp->m_sb.sb_rextsize > 1)
> +
> +	/* Do not free blocks when forcing extent sizes */
> +	if (xfs_inode_has_forcealign(ip) && ip->i_extsize > 1)

I see this sort of check all through the remaining patches.

Given there are significant restrictions on forced alignment,
shouldn't this all the details be pushed inside the helper function?
e.g.

/*
 * Forced extent alignment is dependent on extent size hints being
 * set to define the alignment. Alignment is only necessary when the
 * extent size hint is larger than a single block.
 *
 * If reflink is enabled on the file or we are in always_cow mode,
 * we can't easily do forced alignment.
 *
 * We don't support forced alignment on realtime files.
 * XXX(dgc): why not?
 */
static inline bool
xfs_inode_has_forcealign(struct xfs_inode *ip)
{
	if (!(ip->di_flags & XFS_DIFLAG_EXTSIZE))
		return false;
	if (ip->i_extsize <= 1)
		return false;

	if (xfs_is_cow_inode(ip))
		return false;
	if (ip->di_flags & XFS_DIFLAG_REALTIME)
		return false;

	return ip->di_flags2 & XFS_DIFLAG2_FORCEALIGN;
}

-Dave.
-- 
Dave Chinner
david@...morbit.com