On Wed, Oct 11, 2023 at 07:16:26AM +0200, Christoph Hellwig wrote:
> If xfs_bmapi_write finds a delalloc extent at the requested range, it
> tries to convert the entire delalloc extent to a real allocation.
>
> But if the allocator cannot find a single free extent large enough to
> cover the start block of the requested range, xfs_bmapi_write will
> return 0 but leave *nimaps set to 0.
>
> In that case we simply need to keep looping with the same startoffset_fsb
> so that one of the following allocations will eventually reach the
> requested range.
>
> Note that this could affect any caller of xfs_bmapi_write that covers
> an existing delayed allocation. As far as I can tell we do not have
> any other such caller, though - the regular writeback path uses
> xfs_bmapi_convert_delalloc to convert delayed allocations to real ones,
> and direct I/O invalidates the page cache first.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Looks good,
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> ---
>
> Changes since v1:
> - update comments and the commit log
>
> fs/xfs/xfs_bmap_util.c | 24 +++++++++++++-----------
> 1 file changed, 13 insertions(+), 11 deletions(-)
>
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index d85580b101ad8a..2458be8532c7aa 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -814,12 +814,10 @@ xfs_alloc_file_space(
> {
> xfs_mount_t *mp = ip->i_mount;
> xfs_off_t count;
> - xfs_filblks_t allocated_fsb;
> xfs_filblks_t allocatesize_fsb;
> xfs_extlen_t extsz, temp;
> xfs_fileoff_t startoffset_fsb;
> xfs_fileoff_t endoffset_fsb;
> - int nimaps;
> int rt;
> xfs_trans_t *tp;
> xfs_bmbt_irec_t imaps[1], *imapp;
> @@ -842,7 +840,6 @@ xfs_alloc_file_space(
>
> count = len;
> imapp = &imaps[0];
> - nimaps = 1;
> startoffset_fsb = XFS_B_TO_FSBT(mp, offset);
> endoffset_fsb = XFS_B_TO_FSB(mp, offset + count);
> allocatesize_fsb = endoffset_fsb - startoffset_fsb;
> @@ -853,6 +850,7 @@ xfs_alloc_file_space(
> while (allocatesize_fsb && !error) {
> xfs_fileoff_t s, e;
> unsigned int dblocks, rblocks, resblks;
> + int nimaps = 1;
>
> /*
> * Determine space reservations for data/realtime.
> @@ -918,15 +916,19 @@ xfs_alloc_file_space(
> if (error)
> break;
>
> - allocated_fsb = imapp->br_blockcount;
> -
> - if (nimaps == 0) {
> - error = -ENOSPC;
> - break;
> + /*
> + * If the allocator cannot find a single free extent large
> + * enough to cover the start block of the requested range,
> + * xfs_bmapi_write will return 0 but leave *nimaps set to 0.
> + *
> + * In that case we simply need to keep looping with the same
> + * startoffset_fsb so that one of the following allocations
> + * will eventually reach the requested range.
> + */
> + if (nimaps) {
> + startoffset_fsb += imapp->br_blockcount;
> + allocatesize_fsb -= imapp->br_blockcount;
> }
> -
> - startoffset_fsb += allocated_fsb;
> - allocatesize_fsb -= allocated_fsb;
> }
>
> return error;
> --
> 2.39.2
>
