md: drop queue limitation for RAID1 and RAID10

As suggested by Neil Brown[1], this limitation seems to be
deprecated.

With plugging in use, writes are processed behind the raid thread
and conf->pending_count is not increased. This limitation occurs only
if caller doesn't use plugs.

It can be avoided and often it is (with plugging). There are no reports
that queue is growing to enormous size so remove queue limitation for
non-plugged IOs too.

[1] https://lore.kernel.org/linux-raid/162496301481.7211.18031090130574610495@noble.neil.brown.nameSigned-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
Signed-off-by: Song Liu <song@kernel.org>

drivers/md/raid1-10.c

@@ -22,12 +22,6 @@
 
 #define BIO_SPECIAL(bio) ((unsigned long)bio <= 2)
 
-/* When there are this many requests queue to be written by
- * the raid thread, we become 'congested' to provide back-pressure
- * for writeback.
- */
-static int max_queued_requests = 1024;
-
 /* for managing resync I/O pages */
 struct resync_pages {
 	void		*raid_bio;

drivers/md/raid1.c

@@ -1358,12 +1358,6 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 	r1_bio = alloc_r1bio(mddev, bio);
 	r1_bio->sectors = max_write_sectors;
 
-	if (conf->pending_count >= max_queued_requests) {
-		md_wakeup_thread(mddev->thread);
-		raid1_log(mddev, "wait queued");
-		wait_event(conf->wait_barrier,
-			   conf->pending_count < max_queued_requests);
-	}
 	/* first select target devices under rcu_lock and
 	 * inc refcount on their rdev.  Record them by setting
 	 * bios[x] to bio
@@ -3410,4 +3404,3 @@ MODULE_ALIAS("md-personality-3"); /* RAID1 */
 MODULE_ALIAS("md-raid1");
 MODULE_ALIAS("md-level-1");
 
-module_param(max_queued_requests, int, S_IRUGO|S_IWUSR);

drivers/md/raid10.c

@@ -1387,12 +1387,6 @@ static void raid10_write_request(struct mddev *mddev, struct bio *bio,
 		conf->reshape_safe = mddev->reshape_position;
 	}
 
-	if (conf->pending_count >= max_queued_requests) {
-		md_wakeup_thread(mddev->thread);
-		raid10_log(mddev, "wait queued");
-		wait_event(conf->wait_barrier,
-			   conf->pending_count < max_queued_requests);
-	}
 	/* first select target devices under rcu_lock and
 	 * inc refcount on their rdev.  Record them by setting
 	 * bios[x] to bio
@@ -5243,4 +5237,3 @@ MODULE_ALIAS("md-personality-9"); /* RAID10 */
 MODULE_ALIAS("md-raid10");
 MODULE_ALIAS("md-level-10");
 
-module_param(max_queued_requests, int, S_IRUGO|S_IWUSR);