[PATCH] generic: add gc stress test

[Hans Holmberg <Hans.Holmberg@wdc.com>]

This test stresses garbage collection for file systems by first filling
up a scratch mount to a specific usage point with files of random size,
then doing overwrites in parallel with deletes to fragment the backing
storage, forcing reclaim.

Signed-off-by: Hans Holmberg <hans.holmberg@wdc.com>
---

Test results in my setup (kernel 6.8.0-rc4+)
	f2fs on zoned nullblk: pass (77s)
	f2fs on conventional nvme ssd: pass (13s)
	btrfs on zoned nublk: fails (-ENOSPC)
	btrfs on conventional nvme ssd: fails (-ENOSPC)
	xfs on conventional nvme ssd: pass (8s)

Johannes(cc) is working on the btrfs ENOSPC issue.
	 
 tests/generic/744     | 124 ++++++++++++++++++++++++++++++++++++++++++
 tests/generic/744.out |   6 ++
 2 files changed, 130 insertions(+)
 create mode 100755 tests/generic/744
 create mode 100644 tests/generic/744.out

diff --git a/tests/generic/744 b/tests/generic/744
new file mode 100755
index 000000000000..2c7ab76bf8b1
--- /dev/null
+++ b/tests/generic/744
@@ -0,0 +1,124 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2024 Western Digital Corporation.  All Rights Reserved.
+#
+# FS QA Test No. 744
+#
+# Inspired by btrfs/273 and generic/015
+#
+# This test stresses garbage collection in file systems
+# by first filling up a scratch mount to a specific usage point with
+# files of random size, then doing overwrites in parallel with
+# deletes to fragment the backing zones, forcing reclaim.
+
+. ./common/preamble
+_begin_fstest auto
+
+# real QA test starts here
+
+_require_scratch
+
+# This test requires specific data space usage, skip if we have compression
+# enabled.
+_require_no_compress
+
+M=$((1024 * 1024))
+min_fsz=$((1 * ${M}))
+max_fsz=$((256 * ${M}))
+bs=${M}
+fill_percent=95
+overwrite_percentage=20
+seq=0
+
+_create_file() {
+	local file_name=${SCRATCH_MNT}/data_$1
+	local file_sz=$2
+	local dd_extra=$3
+
+	POSIXLY_CORRECT=yes dd if=/dev/zero of=${file_name} \
+		bs=${bs} count=$(( $file_sz / ${bs} )) \
+		status=none $dd_extra  2>&1
+
+	status=$?
+	if [ $status -ne 0 ]; then
+		echo "Failed writing $file_name" >>$seqres.full
+		exit
+	fi
+}
+
+_total_M() {
+	local total=$(stat -f -c '%b' ${SCRATCH_MNT})
+	local bs=$(stat -f -c '%S' ${SCRATCH_MNT})
+	echo $(( ${total} * ${bs} / ${M}))
+}
+
+_used_percent() {
+	local available=$(stat -f -c '%a' ${SCRATCH_MNT})
+	local total=$(stat -f -c '%b' ${SCRATCH_MNT})
+	echo $((100 - (100 * ${available}) / ${total} ))
+}
+
+
+_delete_random_file() {
+	local to_delete=$(find ${SCRATCH_MNT} -type f | shuf | head -1)
+	rm $to_delete
+	sync ${SCRATCH_MNT}
+}
+
+_get_random_fsz() {
+	local r=$RANDOM
+	echo $(( ${min_fsz} + (${max_fsz} - ${min_fsz}) * (${r} % 100) / 100 ))
+}
+
+_direct_fillup () {
+	while [ $(_used_percent) -lt $fill_percent ]; do
+		local fsz=$(_get_random_fsz)
+
+		_create_file $seq $fsz "oflag=direct conv=fsync"
+		seq=$((${seq} + 1))
+	done
+}
+
+_mixed_write_delete() {
+	local dd_extra=$1
+	local total_M=$(_total_M)
+	local to_write_M=$(( ${overwrite_percentage} * ${total_M} / 100 ))
+	local written_M=0
+
+	while [ $written_M -lt $to_write_M ]; do
+		if [ $(_used_percent) -lt $fill_percent ]; then
+			local fsz=$(_get_random_fsz)
+
+			_create_file $seq $fsz "$dd_extra"
+			written_M=$((${written_M} + ${fsz}/${M}))
+			seq=$((${seq} + 1))
+		else
+			_delete_random_file
+		fi
+	done
+}
+
+seed=$RANDOM
+RANDOM=$seed
+echo "Running test with seed=$seed" >>$seqres.full
+
+_scratch_mkfs_sized $((8 * 1024 * 1024 * 1024)) >>$seqres.full
+_scratch_mount
+
+echo "Starting fillup using direct IO"
+_direct_fillup
+
+echo "Starting mixed write/delete test using direct IO"
+_mixed_write_delete "oflag=direct"
+
+echo "Starting mixed write/delete test using buffered IO"
+_mixed_write_delete ""
+
+echo "Syncing"
+sync ${SCRATCH_MNT}/*
+
+echo "Done, all good"
+
+# success, all done
+status=0
+exit
diff --git a/tests/generic/744.out b/tests/generic/744.out
new file mode 100644
index 000000000000..b40c2f43108e
--- /dev/null
+++ b/tests/generic/744.out
@@ -0,0 +1,6 @@
+QA output created by 744
+Starting fillup using direct IO
+Starting mixed write/delete test using direct IO
+Starting mixed write/delete test using buffered IO
+Syncing
+Done, all good
-- 
2.34.1