On Tue, May 08, 2018 at 01:22:31PM -0400, Brian Foster wrote:
> Unwritten extents by definition have not been written to until they
> are converted to normal written extents. If unwritten extents are
> freed from a file, it is therefore guaranteed that the blocks have
> not been written to since allocation (note that zero range punches
> and reallocates blocks).
>
> To cut down on online discards generated from workloads that make
> use of preallocation, skip discards of extents if they are in the
> unwritten state when the extent is freed.
>
> Note that this optimization does not apply to log recovery, during
> which all freed extents are discarded if online discard is enabled.
> Also note that it may be possible for a filesystem crash to occur
> after write completion of an unwritten extent but before unwritten
> conversion such that the extent remains unwritten after log
> recovery. Since this pseudo-inconsistency may already be possible
> after a crash (consider writing to recently allocated blocks where
> the allocation transaction is lost after a crash), this change
> shouldn't introduce any fundamental limitations that don't already
> exist. In short, on storage stacks where discards are important,
> it's good practice to run an occasional fstrim even with online
> discard enabled in the filesystem, particularly after a crash.
>
> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
Looks ok pending testing,
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
> fs/xfs/libxfs/xfs_bmap.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index dfec27b10e7a..24f60ee810e4 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -5107,7 +5107,8 @@ xfs_bmap_del_extent_real(
> if (error)
> goto done;
> } else {
> - if (bflags & XFS_BMAPI_NODISCARD) {
> + if ((bflags & XFS_BMAPI_NODISCARD) ||
> + (del->br_state == XFS_EXT_UNWRITTEN)) {
> xfs_bmap_add_free_nodiscard(mp, dfops,
> del->br_startblock, del->br_blockcount,
> NULL);
> --
> 2.14.3
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
