2 files changed, 50 insertions, 7 deletions

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index d9869f25aa7..7aa958ed284 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -504,6 +504,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
         unsigned int min_pending;
         struct md_rdev *rdev;
         int choose_first;
+        int choose_next_idle;
 
         rcu_read_lock();
         /*
@@ -520,6 +521,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
         min_pending = UINT_MAX;
         best_good_sectors = 0;
         has_nonrot_disk = 0;
+        choose_next_idle = 0;
 
         if (conf->mddev->recovery_cp < MaxSector &&
             (this_sector + sectors >= conf->next_resync))
@@ -532,6 +534,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
                 sector_t first_bad;
                 int bad_sectors;
                 unsigned int pending;
+                bool nonrot;
 
                 rdev = rcu_dereference(conf->mirrors[disk].rdev);
                 if (r1_bio->bios[disk] == IO_BLOCKED
@@ -590,18 +593,52 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
                 } else
                         best_good_sectors = sectors;
 
-                has_nonrot_disk |= blk_queue_nonrot(bdev_get_queue(rdev->bdev));
+                nonrot = blk_queue_nonrot(bdev_get_queue(rdev->bdev));
+                has_nonrot_disk |= nonrot;
                 pending = atomic_read(&rdev->nr_pending);
                 dist = abs(this_sector - conf->mirrors[disk].head_position);
-                if (choose_first
-                    /* Don't change to another disk for sequential reads */
-                    || conf->mirrors[disk].next_seq_sect == this_sector
-                    || dist == 0
-                    /* If device is idle, use it */
-                    || pending == 0) {
+                if (choose_first) {
                         best_disk = disk;
                         break;
                 }
+                /* Don't change to another disk for sequential reads */
+                if (conf->mirrors[disk].next_seq_sect == this_sector
+                    || dist == 0) {
+                        int opt_iosize = bdev_io_opt(rdev->bdev) >> 9;
+                        struct raid1_info *mirror = &conf->mirrors[disk];
+
+                        best_disk = disk;
+                        /*
+                         * If buffered sequential IO size exceeds optimal
+                         * iosize, check if there is idle disk. If yes, choose
+                         * the idle disk. read_balance could already choose an
+                         * idle disk before noticing it's a sequential IO in
+                         * this disk. This doesn't matter because this disk
+                         * will idle, next time it will be utilized after the
+                         * first disk has IO size exceeds optimal iosize. In
+                         * this way, iosize of the first disk will be optimal
+                         * iosize at least. iosize of the second disk might be
+                         * small, but not a big deal since when the second disk
+                         * starts IO, the first disk is likely still busy.
+                         */
+                        if (nonrot && opt_iosize > 0 &&
+                            mirror->seq_start != MaxSector &&
+                            mirror->next_seq_sect > opt_iosize &&
+                            mirror->next_seq_sect - opt_iosize >=
+                            mirror->seq_start) {
+                                choose_next_idle = 1;
+                                continue;
+                        }
+                        break;
+                }
+                /* If device is idle, use it */
+                if (pending == 0) {
+                        best_disk = disk;
+                        break;
+                }
+
+                if (choose_next_idle)
+                        continue;
 
                 if (min_pending > pending) {
                         min_pending = pending;
@@ -640,6 +677,10 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
                         goto retry;
                 }
                 sectors = best_good_sectors;
+
+                if (conf->mirrors[best_disk].next_seq_sect != this_sector)
+                        conf->mirrors[best_disk].seq_start = this_sector;
+
                 conf->mirrors[best_disk].next_seq_sect = this_sector + sectors;
         }
         rcu_read_unlock();
@@ -2605,6 +2646,7 @@ static struct r1conf *setup_conf(struct mddev *mddev)
                         mddev->merge_check_needed = 1;
 
                 disk->head_position = 0;
+                disk->seq_start = MaxSector;
         }
         conf->raid_disks = mddev->raid_disks;
         conf->mddev = mddev;
diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
index 3770b4a2766..0ff3715fb7e 100644
--- a/drivers/md/raid1.h
+++ b/drivers/md/raid1.h
@@ -9,6 +9,7 @@ struct raid1_info {
          * we try to keep sequential reads one the same device
          */
         sector_t        next_seq_sect;
+        sector_t        seq_start;
 };
 
 /*