[PATCH] loop: add WQ_MEM_RECLAIM flag to per device workqueue

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Commit b5dd2f6047ca1080 ("block: loop: improve performance via blk-mq")
started using a global WQ_MEM_RECLAIM workqueue.

+       loop_wq = alloc_workqueue("kloopd",
+                       WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0);

Commit f4aa4c7bbac6c4af ("block: loop: convert to per-device workqueue")
started using per device WQ_MEM_RECLAIM workqueue.

-       loop_wq = alloc_workqueue("kloopd",
-                       WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0);
+       lo->wq = alloc_workqueue("kloopd%d",
+                       WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0,
+                       lo->lo_number);

Commit 4d4e41aef9429872 ("block: loop: avoiding too many pending per work
I/O") adjusted max_active parameter.

-                       WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0,
+                       WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 16,

Commit e03a3d7a94e2485b ("block: loop: use kthread_work") started using
per device kthread.

-       lo->wq = alloc_workqueue("kloopd%d",
-                       WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 16,
-                       lo->lo_number);
+       lo->worker_task = kthread_run(kthread_worker_fn,
+                       &lo->worker, "loop%d", lo->lo_number);

Commit 87579e9b7d8dc36e ("loop: use worker per cgroup instead of kworker")
again started using per device workqueue

-       lo->worker_task = kthread_run(loop_kthread_worker_fn,
-                       &lo->worker, "loop%d", lo->lo_number);
+       lo->workqueue = alloc_workqueue("loop%d",
+                                       WQ_UNBOUND | WQ_FREEZABLE,
+                                       0,
+                                       lo->lo_number);

but forgot to restore WQ_MEM_RECLAIM flag.

We should reserve one "struct task_struct" to each loop device in order
to guarantee that I/O request for writeback operation can make forward
progress even under memory pressure. I don't know why WQ_FREEZABLE flag
was added, but let's add WQ_MEM_RECLAIM flag like commit f4aa4c7bbac6c4af
("block: loop: convert to per-device workqueue") describes.

Fixes: 87579e9b7d8dc36e ("loop: use worker per cgroup instead of kworker")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 drivers/block/loop.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 19fe19eaa50e..60dfebcedd95 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1013,7 +1013,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
 		lo->lo_flags |= LO_FLAGS_READ_ONLY;
 
 	lo->workqueue = alloc_workqueue("loop%d",
-					WQ_UNBOUND | WQ_FREEZABLE,
+					WQ_MEM_RECLAIM | WQ_UNBOUND | WQ_FREEZABLE,
 					0,
 					lo->lo_number);
 	if (!lo->workqueue) {
-- 
2.32.0