[PATCH] tests: add a new test to check if pluged bio is unlimited for raid10

[Yu Kuai <yukuai1@huaweicloud.com>]

From: Yu Kuai <yukuai3@huawei.com>

Pluged bio is unlimited means that all submitted bio will be pluged, and
those bio won't be issued to underlaying disks until blk_finish_plug() or
blk_flush_plug(). In this case, a lot memory will be used for
raid10_bio and io latency will be very bad.

This test do some dirty pages writeback for raid10, where plug is used, and
check if device inflight counter exceed threshold.

This problem is supposed to be fixed by [1].

[1] https://lore.kernel.org/linux-raid/20230420112946.2869956-9-yukuai1@huaweicloud.com/

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 tests/22raid10plug | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 tests/22raid10plug

diff --git a/tests/22raid10plug b/tests/22raid10plug
new file mode 100644
index 00000000..fde4ce80
--- /dev/null
+++ b/tests/22raid10plug
@@ -0,0 +1,41 @@
+devs="$dev0 $dev1 $dev2 $dev3 $dev4 $dev5"
+
+# test will fail if inflight is observed to be greater
+threshold=4096
+
+# create a simple raid10
+mdadm --create --run --level=raid10 --raid-disks 6 $md0 $devs --bitmap=internal --assume-clean
+if [ $? -ne 0 ]; then
+        die "create raid10 failed"
+fi
+
+old_background=`cat /proc/sys/vm/dirty_background_ratio`
+old=`cat /proc/sys/vm/dirty_ratio`
+
+# trigger background writeback
+echo 0 > /proc/sys/vm/dirty_background_ratio
+echo 60 > /proc/sys/vm/dirty_ratio
+
+# io pressure with buffer write
+fio -filename=$md0 -ioengine=libaio -rw=write -bs=4k -numjobs=1 -iodepth=128 -name=test -runtime=10 &
+
+pid=$!
+
+sleep 2
+
+# check if inflight exceed threshold
+while true; do
+        tmp=`cat /sys/block/md0/inflight | awk '{printf("%d\n", $1 + $2);}'`
+        if [ $tmp -gt $threshold ]; then
+                die "inflight is greater than 4096"
+                break
+        elif [ $tmp -eq 0 ]; then
+                break
+        fi
+        sleep 0.1
+done
+
+kill -9 $pid
+mdadm -S $md0
+echo $old_background > /proc/sys/vm/dirty_background_ratio
+echo $old > /proc/sys/vm/dirty_ratio
-- 
2.39.2