Re: [PATCH 4/9] xfs: only reserve quota blocks for bmbt changes if we're changing the data fork

Brian Foster
2020-06-25T12:28:06Z

On Wed, Jun 24, 2020 at 06:18:06PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
>
> Now that we've reworked xfs_reflink_remap_extent to remap only one
> extent per transaction, we actually know if the extent being removed is
> an allocated mapping. This means that we now know ahead of time if
> we're going to be touching the data fork.
>
> Since we only need blocks for a bmbt split if we're going to update the
> data fork, we only need to get quota reservation if we know we're going
> to touch the data fork.
>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---

That addresses my question on the previous patch. Looks like the qres
check was just misplaced. NBD:

Reviewed-by: Brian Foster <bfoster@redhat.com>

> fs/xfs/xfs_reflink.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
>
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index c593d52156df..9cc1c340d0ec 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -1043,7 +1043,11 @@ xfs_reflink_remap_extent(
> * Compute quota reservation if we think the quota block counter for
> * this file could increase.
> *
> - * We start by reserving enough blocks to handle a bmbt split.
> + * Adding a written extent to the extent map can cause a bmbt split,
> + * and removing a mapped extent from the extent can cause a bmbt split.
> + * The two operations cannot both cause a split since they operate on
> + * the same index in the bmap btree, so we only need a reservation for
> + * one bmbt split if either thing is happening.
> *
> * If we are mapping a written extent into the file, we need to have
> * enough quota block count reservation to handle the blocks in that
> @@ -1056,8 +1060,9 @@ xfs_reflink_remap_extent(
> * before we started. That should have removed all the delalloc
> * reservations, but we code defensively.
> */
> - qdelta = 0;
> - qres = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
> + qres = qdelta = 0;
> + if (smap_mapped || dmap_written)
> + qres = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
> if (dmap_written)
> qres += dmap->br_blockcount;
> if (qres > 0) {
>