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

Darrick J. Wong
2024-06-24T15:54:44Z

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
>
>