Re: [PATCH 10/10] xfs: reclaim speculative preallocations for append only files

["Darrick J. Wong" <djwong@kernel.org>]

On Sun, Jun 23, 2024 at 07:34:55AM +0200, Christoph Hellwig wrote:
> The XFS XFS_DIFLAG_APPEND maps to the VFS S_APPEND flag, which forbids
> writes that don't append at the current EOF.
> 
> But the commit originally adding XFS_DIFLAG_APPEND support (commit
> a23321e766d in xfs xfs-import repository) also checked it to skip
> releasing speculative preallocations, which doesn't make any sense.
> 
> Another commit (dd9f438e3290 in the xfs-import repository) late extended

                                                             later

> that flag to also report these speculation preallocations which should
> not exist in getbmap.
> 
> Remove these checks as nothing XFS_DIFLAG_APPEND implies that
> preallocations beyond EOF should exist, but explicitly check for
> XFS_DIFLAG_APPEND in xfs_file_release to bypass the algorithm that
> discard preallocations on the first close as append only file aren't

                                                           files

> expected to be written to only once.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/xfs_bmap_util.c | 12 +++++-------
>  fs/xfs/xfs_file.c      |  4 ++++
>  fs/xfs/xfs_icache.c    |  2 +-
>  3 files changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index 52863b784b023f..aa924d7cd32abd 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -331,8 +331,7 @@ xfs_getbmap(
>  		}
>  
>  		if (xfs_get_extsz_hint(ip) ||
> -		    (ip->i_diflags &
> -		     (XFS_DIFLAG_PREALLOC | XFS_DIFLAG_APPEND)))
> +		    (ip->i_diflags & XFS_DIFLAG_PREALLOC))

The last time you tried to remove XFS_DIFLAG_APPEND from this test, I
noticed that there's some fstest that "fails" because the bmap output
for an append-only file now stops at isize instead of maxbytes.  Do you
see this same regression?

>  			max_len = mp->m_super->s_maxbytes;
>  		else
>  			max_len = XFS_ISIZE(ip);
> @@ -524,12 +523,11 @@ xfs_can_free_eofblocks(
>  		return false;
>  
>  	/*
> -	 * Only free real extents for inodes with persistent preallocations or
> -	 * the append-only flag.
> +	 * Do not free real extents in preallocated files unless the file has
> +	 * delalloc blocks and we are forced to remove them.
>  	 */
> -	if (ip->i_diflags & (XFS_DIFLAG_PREALLOC | XFS_DIFLAG_APPEND))
> -		if (ip->i_delayed_blks == 0)
> -			return false;
> +	if ((ip->i_diflags & XFS_DIFLAG_PREALLOC) && !ip->i_delayed_blks)
> +		return false;
>  
>  	/*
>  	 * Do not try to free post-EOF blocks if EOF is beyond the end of the
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 1903fa5568a37d..b05822a70ea680 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1231,6 +1231,9 @@ xfs_file_release(
>  	 * one file after another without going back to it while keeping the
>  	 * preallocation for files that have recurring open/write/close cycles.
>  	 *
> +	 * This heuristic is skipped for inodes with the append-only flag as
> +	 * that flags is rather pointless for inodes written oly once.

                flag                                         only

--D

> +	 *
>  	 * There is no point in freeing blocks here for open but unlinked files
>  	 * as they will be taken care of by the inactivation path soon.
>  	 *
> @@ -1245,6 +1248,7 @@ xfs_file_release(
>  	 */
>  	if (inode->i_nlink &&
>  	    (file->f_mode & FMODE_WRITE) &&
> +	    !(ip->i_diflags & XFS_DIFLAG_APPEND) &&
>  	    !xfs_iflags_test(ip, XFS_EOFBLOCKS_RELEASED) &&
>  	    xfs_ilock_nowait(ip, XFS_IOLOCK_EXCL)) {
>  		if (xfs_can_free_eofblocks(ip)) {
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index 9967334ea99f1a..0f07ec842b7023 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
> @@ -1158,7 +1158,7 @@ xfs_inode_free_eofblocks(
>  	if (xfs_can_free_eofblocks(ip))
>  		return xfs_free_eofblocks(ip);
>  
> -	/* inode could be preallocated or append-only */
> +	/* inode could be preallocated */
>  	trace_xfs_inode_free_eofblocks_invalid(ip);
>  	xfs_inode_clear_eofblocks_tag(ip);
>  	return 0;
> -- 
> 2.43.0
> 
>