[PATCH] md: skip redundant raid_disks update when value is unchanged

[Abd-Alrhman Masalkhi]

Calling update_raid_disks() with the same value as the current one
can trigger unnecessary work. For example, RAID1 will reallocate
resources such as the mempool for r1bio.

Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@xxxxxxxxx>
---
It returns -EINVAL for the same value. If silent success is preferred
instead, please let me know so I adjust its behavior.
---
 drivers/md/md.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 0e55639211f2..cb66c4ebbafa 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4409,9 +4409,12 @@ raid_disks_store(struct mddev *mddev, const char *buf, size_t len)
 	err = mddev_suspend_and_lock(mddev);
 	if (err)
 		return err;
-	if (mddev->pers)
-		err = update_raid_disks(mddev, n);
-	else if (mddev->reshape_position != MaxSector) {
+	if (mddev->pers) {
+		if (n != mddev->raid_disks)
+			err = update_raid_disks(mddev, n);
+		else
+			err = -EINVAL;
+	} else if (mddev->reshape_position != MaxSector) {
 		struct md_rdev *rdev;
 		int olddisks = mddev->raid_disks - mddev->delta_disks;
 
-- 
2.43.0