Re: [PATCH 5/9] xfs: only reserve quota blocks if we're mapping into a hole

[Brian Foster <bfoster@redhat.com>]

On Wed, Jun 24, 2020 at 06:18:12PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> When logging quota block count updates during a reflink operation, we
> only log the /delta/ of the block count changes to the dquot.  Since we
> now know ahead of time the extent type of both dmap and smap (and that
> they have the same length), we know that we only need to reserve quota
> blocks for dmap's blockcount if we're mapping it into a hole.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---

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

>  fs/xfs/xfs_reflink.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> 
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 9cc1c340d0ec..72de7179399d 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -1051,7 +1051,9 @@ xfs_reflink_remap_extent(
>  	 *
>  	 * 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
> -	 * extent.
> +	 * extent.  We log only the delta to the quota block counts, so if the
> +	 * extent we're unmapping also has blocks allocated to it, we don't
> +	 * need a quota reservation for the extent itself.
>  	 *
>  	 * Note that if we're replacing a delalloc reservation with a written
>  	 * extent, we have to take the full quota reservation because removing
> @@ -1063,7 +1065,7 @@ xfs_reflink_remap_extent(
>  	qres = qdelta = 0;
>  	if (smap_mapped || dmap_written)
>  		qres = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
> -	if (dmap_written)
> +	if (!smap_mapped && dmap_written)
>  		qres += dmap->br_blockcount;
>  	if (qres > 0) {
>  		error = xfs_trans_reserve_quota_nblks(tp, ip, qres, 0,
>