btrfs: defrag with compressed extents

There is a long existing bug in btrfs defrag code that it will
always try to defrag compressed extents, even they are already at
max capacity.

This will not reduce the number of extents, but only waste IO/CPU.

The kernel fix is titled:

  btrfs: defrag: don't defrag extents which is already at its max capacity

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

diff --git a/tests/btrfs/259 b/tests/btrfs/259
new file mode 100755 (executable)
index 0000000..e7bd8dd
--- /dev/null
+++ b/tests/btrfs/259
@@ -0,0 +1,57 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2022 SUSE Linux Products GmbH. All Rights Reserved.
+#
+# FS QA Test 259
+#
+# Make sure btrfs defrag ioctl won't defrag compressed extents which are already
+# at their max capacity.
+#
+. ./common/preamble
+_begin_fstest auto quick defrag
+
+# Import common functions.
+. ./common/filter
+. ./common/btrfs
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs btrfs
+_require_scratch
+
+_scratch_mkfs >> $seqres.full
+
+_scratch_mount -o compress
+
+# Btrfs uses 128K as max extent size for compressed extents, this would result
+# several compressed extents all at their max size
+$XFS_IO_PROG -f -c "pwrite -S 0xee 0 16m" -c sync \
+       $SCRATCH_MNT/foobar >> $seqres.full
+
+old_csum=$(_md5_checksum $SCRATCH_MNT/foobar)
+
+echo "=== File extent layout before defrag ===" >> $seqres.full
+$XFS_IO_PROG -c "fiemap -v" "$SCRATCH_MNT/foobar" >> $seqres.full
+$XFS_IO_PROG -c "fiemap -v" "$SCRATCH_MNT/foobar" > $tmp.before
+
+$BTRFS_UTIL_PROG filesystem defrag "$SCRATCH_MNT/foobar" >> $seqres.full
+sync
+
+new_csum=$(_md5_checksum $SCRATCH_MNT/foobar)
+
+echo "=== File extent layout before defrag ===" >> $seqres.full
+$XFS_IO_PROG -c "fiemap -v" "$SCRATCH_MNT/foobar" >> $seqres.full
+$XFS_IO_PROG -c "fiemap -v" "$SCRATCH_MNT/foobar" > $tmp.after
+
+if [ $new_csum != $old_csum ]; then
+       echo "file content changed"
+fi
+
+diff -q $tmp.before $tmp.after || echo "compressed extents get defragged"
+
+echo "Silence is golden"
+
+# success, all done
+status=0
+exit

diff --git a/tests/btrfs/259.out b/tests/btrfs/259.out
new file mode 100644 (file)
index 0000000..bfbd2de
--- /dev/null
+++ b/tests/btrfs/259.out
@@ -0,0 +1,2 @@
+QA output created by 259
+Silence is golden