md/raid1: factor out choose_slow_rdev() from read_balance()

read_balance() is hard to understand because there are too many status
and branches, and it's overlong.

This patch factor out the case to read the slow rdev from
read_balance(), there are no functional changes.

Co-developed-by: Paul Luse <paul.e.luse@linux.intel.com>
Signed-off-by: Paul Luse <paul.e.luse@linux.intel.com>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20240229095714.926789-9-yukuai1@huaweicloud.com

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 3149f22f1155aef1d933887e8e994f54c9925aae..09b7e93a54b5660a5bfa67114123187c33b6edca 100644 (file)
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -620,6 +620,53 @@ static int choose_first_rdev(struct r1conf *conf, struct r1bio *r1_bio,
        return -1;
 }
 
+static int choose_slow_rdev(struct r1conf *conf, struct r1bio *r1_bio,
+                           int *max_sectors)
+{
+       sector_t this_sector = r1_bio->sector;
+       int bb_disk = -1;
+       int bb_read_len = 0;
+       int disk;
+
+       for (disk = 0 ; disk < conf->raid_disks * 2 ; disk++) {
+               struct md_rdev *rdev;
+               int len;
+               int read_len;
+
+               if (r1_bio->bios[disk] == IO_BLOCKED)
+                       continue;
+
+               rdev = conf->mirrors[disk].rdev;
+               if (!rdev || test_bit(Faulty, &rdev->flags) ||
+                   !test_bit(WriteMostly, &rdev->flags))
+                       continue;
+
+               /* there are no bad blocks, we can use this disk */
+               len = r1_bio->sectors;
+               read_len = raid1_check_read_range(rdev, this_sector, &len);
+               if (read_len == r1_bio->sectors) {
+                       update_read_sectors(conf, disk, this_sector, read_len);
+                       return disk;
+               }
+
+               /*
+                * there are partial bad blocks, choose the rdev with largest
+                * read length.
+                */
+               if (read_len > bb_read_len) {
+                       bb_disk = disk;
+                       bb_read_len = read_len;
+               }
+       }
+
+       if (bb_disk != -1) {
+               *max_sectors = bb_read_len;
+               update_read_sectors(conf, bb_disk, this_sector, bb_read_len);
+       }
+
+       return bb_disk;
+}
+
 /*
  * This routine returns the disk from which the requested read should
  * be done. There is a per-array 'next expected sequential IO' sector
@@ -673,23 +720,8 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
                if (!test_bit(In_sync, &rdev->flags) &&
                    rdev->recovery_offset < this_sector + sectors)
                        continue;
-               if (test_bit(WriteMostly, &rdev->flags)) {
-                       /* Don't balance among write-mostly, just
-                        * use the first as a last resort */
-                       if (best_dist_disk < 0) {
-                               if (is_badblock(rdev, this_sector, sectors,
-                                               &first_bad, &bad_sectors)) {
-                                       if (first_bad <= this_sector)
-                                               /* Cannot use this */
-                                               continue;
-                                       best_good_sectors = first_bad - this_sector;
-                               } else
-                                       best_good_sectors = sectors;
-                               best_dist_disk = disk;
-                               best_pending_disk = disk;
-                       }
+               if (test_bit(WriteMostly, &rdev->flags))
                        continue;
-               }
                /* This is a reasonable device to use.  It might
                 * even be best.
                 */
@@ -808,7 +840,10 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
        }
        *max_sectors = sectors;
 
-       return best_disk;
+       if (best_disk >= 0)
+               return best_disk;
+
+       return choose_slow_rdev(conf, r1_bio, max_sectors);
 }
 
 static void wake_up_barrier(struct r1conf *conf)