From 84ca484ecf2f8e1dc3afddc895cb9b62c531db49 Mon Sep 17 00:00:00 2001 From: Brian Foster Date: Wed, 9 May 2018 08:45:05 -0700 Subject: [PATCH] xfs: don't discard on free of unwritten extents 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 Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong --- 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 534ffb856c4a..3d7c53db1977 100644 --- a/fs/xfs/libxfs/xfs_bmap.c +++ b/fs/xfs/libxfs/xfs_bmap.c @@ -5109,7 +5109,8 @@ 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);