On Sun, Jan 23, 2022 at 01:31:33PM +0800, Qu Wenruo wrote: > Recent v5.16 has some regression around btrfs autodefrag mount option, > and the extra scrutiny around defrag code exposes some questionable > behavior from the old code. > > One behavior is to defrag extents along with the next preallocated > extent. > > This behavior will cause extra IO and convert all the preallocated > extent to regular zero filled extents, rendering the preallocated extent > useless. > > The kernel fix is titled: > > btrfs: defrag: don't try to merge regular extents with preallocated extents > > Signed-off-by: Qu Wenruo <wqu@xxxxxxxx> > --- > tests/btrfs/255 | 81 +++++++++++++++++++++++++++++++++++++++++++++ > tests/btrfs/255.out | 2 ++ > 2 files changed, 83 insertions(+) > create mode 100755 tests/btrfs/255 > create mode 100644 tests/btrfs/255.out > > diff --git a/tests/btrfs/255 b/tests/btrfs/255 > new file mode 100755 > index 00000000..3d952c1f > --- /dev/null > +++ b/tests/btrfs/255 > @@ -0,0 +1,81 @@ > +#! /bin/bash > +# SPDX-License-Identifier: GPL-2.0 > +# Copyright (C) 2022 SUSE Linux Products GmbH. All Rights Reserved. > +# > +# FS QA Test 255 > +# > +# Make sure btrfs doesn't defrag preallocated extents, nor lone extents > +# before preallocated extents. > +# > + > +. ./common/preamble > +_begin_fstest auto quick defrag > + > +# Override the default cleanup function. > +# _cleanup() > +# { > +# cd / > +# rm -r -f $tmp.* > +# } > + > +# Import common functions. > +. ./common/filter > + > +# real QA test starts here > + > +# Modify as appropriate. > +_supported_fs btrfs > +_require_scratch > + > +get_extent_disk_sector() > +{ > + local file=$1 > + local offset=$2 > + > + $XFS_IO_PROG -c "fiemap $offset" "$file" | _filter_xfs_io_fiemap |\ > + head -n1 | awk '{print $3}' awk -> $AWK_PROG > +} > +# Needs 4K sectorsize > +_scratch_mkfs -s 4k >> $seqres.full 2>&1 Shouldn't it be a require rule so that it doesn't fail in some weird way in case it's running a machine with a page size > 4K and on a kernel without subpage size support? > + > +# Need datacow to make the defragged extents to have different bytenr > +_scratch_mount -o datacow > + > +# Create a file with the following layout: > +# 0 4K 8K 16K > +# |<- R ->|<-- Preallocated ->| > +# R is regular extents. > +# > +# In this case it makes no sense to defrag any extent. > +$XFS_IO_PROG -f -c "pwrite 0 4k" -c sync -c "falloc 4k 12k" \ > + "$SCRATCH_MNT/foobar" >> $seqres.full > + > +echo "=== Initial file extent layout ===" >> $seqres.full > +$XFS_IO_PROG -c "fiemap -v" "$SCRATCH_MNT/foobar" >> $seqres.full > + > +# Save the bytenr of both extents > +old_regular=$(get_extent_disk_sector "$SCRATCH_MNT/foobar" 0) > +old_prealloc=$(get_extent_disk_sector "$SCRATCH_MNT/foobar" 4096) > + > +# Now defrag and write the defragged range back to disk > +$BTRFS_UTIL_PROG filesystem defrag "$SCRATCH_MNT/foobar" >> $seqres.full > +sync > + > +echo "=== File extent layout after defrag ===" >> $seqres.full > +$XFS_IO_PROG -c "fiemap -v" "$SCRATCH_MNT/foobar" >> $seqres.full > + > +new_regular=$(get_extent_disk_sector "$SCRATCH_MNT/foobar" 0) > +new_prealloc=$(get_extent_disk_sector "$SCRATCH_MNT/foobar" 4096) > + > +if [ "$old_regular" -ne "$new_regular" ]; then > + echo "the single lone sector get defragged" get -> got > +fi > +if [ "$old_prealloc" -ne "$new_prealloc" ]; then > + echo "the preallocated extent get defragged" get -> got Otherwise it looks good, thanks. > +fi > + > +echo "Silence is golden" > + > +# success, all done > +status=0 > +exit > diff --git a/tests/btrfs/255.out b/tests/btrfs/255.out > new file mode 100644 > index 00000000..7eefb828 > --- /dev/null > +++ b/tests/btrfs/255.out > @@ -0,0 +1,2 @@ > +QA output created by 255 > +Silence is golden > -- > 2.34.1 >