md: factor out a helper raid_is_456()

JIRA: https://issues.redhat.com/browse/RHEL-123668

commit 7797da1
Author: Yu Kuai <yukuai3@huawei.com>
Date:   Fri Aug 29 16:04:17 2025 +0800

    md: factor out a helper raid_is_456()

    There are no functional changes, the helper will be used by llbitmap in
    following patches.

    Link: https://lore.kernel.org/linux-raid/20250829080426.1441678-3-yukuai1@huaweicloud.com
    Signed-off-by: Yu Kuai <yukuai3@huawei.com>
    Reviewed-by: Xiao Ni <xni@redhat.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Reviewed-by: Hannes Reinecke <hare@suse.de>
    Reviewed-by: Li Nan <linan122@huawei.com>

Signed-off-by: Nigel Croxon <ncroxon@redhat.com>

Author: ncroxon

drivers/md/md.c

@@ -9084,19 +9084,12 @@ static sector_t md_sync_position(struct mddev *mddev, enum sync_action action)
 
 static bool sync_io_within_limit(struct mddev *mddev)
 {
-	int io_sectors;
-
 	/*
 	 * For raid456, sync IO is stripe(4k) per IO, for other levels, it's
 	 * RESYNC_PAGES(64k) per IO.
 	 */
-	if (mddev->level == 4 || mddev->level == 5 || mddev->level == 6)
-		io_sectors = 8;
-	else
-		io_sectors = 128;
-
 	return atomic_read(&mddev->recovery_active) <
-		io_sectors * sync_io_depth(mddev);
+	       (raid_is_456(mddev) ? 8 : 128) * sync_io_depth(mddev);
 }
 
 #define SYNC_MARKS	10

drivers/md/md.h

@@ -1034,6 +1034,12 @@ static inline bool mddev_is_dm(struct mddev *mddev)
 	return !mddev->gendisk;
 }
 
+static inline bool raid_is_456(struct mddev *mddev)
+{
+	return mddev->level == ID_RAID4 || mddev->level == ID_RAID5 ||
+	       mddev->level == ID_RAID6;
+}
+
 static inline void mddev_trace_remap(struct mddev *mddev, struct bio *bio,
 		sector_t sector)
 {