[PATCH 2/2] bcache: Move journal work to new background wq

[Kai Krakow <kai@xxxxxxxxxxx>]

This is potentially long running and not latency sensitive, let's get
it out of the way of other latency sensitive events.

As observed in the previous commit, the system_wq comes easily
congested by bcache, and this fixes a few more stalls I was observing
every once in a while.

Cc: Coly Li <colyli@xxxxxxx>
Signed-off-by: Kai Krakow <kai@xxxxxxxxxxx>
---
 drivers/md/bcache/bcache.h  | 1 +
 drivers/md/bcache/journal.c | 4 ++--
 drivers/md/bcache/super.c   | 7 +++++++
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index b1ed16c7a5341..70565ed5732d7 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -1001,6 +1001,7 @@ void bch_write_bdev_super(struct cached_dev *dc, struct closure *parent);
 
 extern struct workqueue_struct *bcache_wq;
 extern struct workqueue_struct *bch_journal_wq;
+extern struct workqueue_struct *bch_background_wq;
 extern struct mutex bch_register_lock;
 extern struct list_head bch_cache_sets;
 
diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
index aefbdb7e003bc..942e97dd17554 100644
--- a/drivers/md/bcache/journal.c
+++ b/drivers/md/bcache/journal.c
@@ -932,8 +932,8 @@ atomic_t *bch_journal(struct cache_set *c,
 		journal_try_write(c);
 	} else if (!w->dirty) {
 		w->dirty = true;
-		schedule_delayed_work(&c->journal.work,
-				      msecs_to_jiffies(c->journal_delay_ms));
+		queue_delayed_work(bch_background_wq, &c->journal.work,
+				   msecs_to_jiffies(c->journal_delay_ms));
 		spin_unlock(&c->journal.lock);
 	} else {
 		spin_unlock(&c->journal.lock);
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index dc4fe7eeda815..9e1481917ce6a 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -49,6 +49,7 @@ static int bcache_major;
 static DEFINE_IDA(bcache_device_idx);
 static wait_queue_head_t unregister_wait;
 struct workqueue_struct *bcache_wq;
+struct workqueue_struct *bch_background_wq;
 struct workqueue_struct *bch_journal_wq;
 
 
@@ -2822,6 +2823,8 @@ static void bcache_exit(void)
 		destroy_workqueue(bcache_wq);
 	if (bch_journal_wq)
 		destroy_workqueue(bch_journal_wq);
+	if (bch_background_wq)
+		destroy_workqueue(bch_background_wq);
 
 	if (bcache_major)
 		unregister_blkdev(bcache_major, "bcache");
@@ -2884,6 +2887,10 @@ static int __init bcache_init(void)
 	if (bch_btree_init())
 		goto err;
 
+	bch_background_wq = alloc_workqueue("bch_background", 0, 0);
+	if (!bch_background_wq)
+		goto err;
+
 	bch_journal_wq = alloc_workqueue("bch_journal", WQ_MEM_RECLAIM, 0);
 	if (!bch_journal_wq)
 		goto err;
-- 
2.26.2