md: simplify raid10 read_balance

raid10 read balance has two different loop for looking through
possible devices to chose the best.
Collapse those into one loop and generally make the code more
readable.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 44 insertions, 66 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 8e9462626ec5..8ea0acad606b 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -488,13 +488,19 @@ static int raid10_mergeable_bvec(struct request_queue *q,
 static int read_balance(conf_t *conf, r10bio_t *r10_bio)
 {
         const sector_t this_sector = r10_bio->sector;
-        int disk, slot, nslot;
+        int disk, slot;
         const int sectors = r10_bio->sectors;
-        sector_t new_distance, current_distance;
+        sector_t new_distance, best_dist;
         mdk_rdev_t *rdev;
+        int do_balance;
+        int best_slot;
 
         raid10_find_phys(conf, r10_bio);
         rcu_read_lock();
+retry:
+        best_slot = -1;
+        best_dist = MaxSector;
+        do_balance = 1;
         /*
          * Check if we can balance. We can balance on the whole
          * device if no resync is going on (recovery is ok), or below
@@ -502,86 +508,58 @@ static int read_balance(conf_t *conf, r10bio_t *r10_bio)
          * above the resync window.
          */
         if (conf->mddev->recovery_cp < MaxSector
-            && (this_sector + sectors >= conf->next_resync)) {
-                /* make sure that disk is operational */
-                slot = 0;
-                disk = r10_bio->devs[slot].devnum;
-
-                while ((rdev = rcu_dereference(conf->mirrors[disk].rdev)) == NULL ||
-                       r10_bio->devs[slot].bio == IO_BLOCKED ||
-                       !test_bit(In_sync, &rdev->flags)) {
-                        slot++;
-                        if (slot == conf->copies) {
-                                slot = 0;
-                                disk = -1;
-                                break;
-                        }
-                        disk = r10_bio->devs[slot].devnum;
-                }
-                goto rb_out;
-        }
-
+            && (this_sector + sectors >= conf->next_resync))
+                do_balance = 0;
 
-        /* make sure the disk is operational */
-        slot = 0;
-        disk = r10_bio->devs[slot].devnum;
-        while ((rdev=rcu_dereference(conf->mirrors[disk].rdev)) == NULL ||
-               r10_bio->devs[slot].bio == IO_BLOCKED ||
-               !test_bit(In_sync, &rdev->flags)) {
-                slot ++;
-                if (slot == conf->copies) {
-                        disk = -1;
-                        goto rb_out;
-                }
+        for (slot = 0; slot < conf->copies ; slot++) {
+                if (r10_bio->devs[slot].bio == IO_BLOCKED)
+                        continue;
                 disk = r10_bio->devs[slot].devnum;
-        }
-
-
-        current_distance = abs(r10_bio->devs[slot].addr -
-                               conf->mirrors[disk].head_position);
-
-        /* Find the disk whose head is closest,
-         * or - for far > 1 - find the closest to partition beginning */
-
-        for (nslot = slot; nslot < conf->copies; nslot++) {
-                int ndisk = r10_bio->devs[nslot].devnum;
-
-
-                if ((rdev=rcu_dereference(conf->mirrors[ndisk].rdev)) == NULL ||
-                    r10_bio->devs[nslot].bio == IO_BLOCKED ||
-                    !test_bit(In_sync, &rdev->flags))
+                rdev = rcu_dereference(conf->mirrors[disk].rdev);
+                if (rdev == NULL)
+                        continue;
+                if (!test_bit(In_sync, &rdev->flags))
                         continue;
 
+                if (!do_balance)
+                        break;
+
                 /* This optimisation is debatable, and completely destroys
                  * sequential read speed for 'far copies' arrays.  So only
                  * keep it for 'near' arrays, and review those later.
                  */
-                if (conf->near_copies > 1 && !atomic_read(&rdev->nr_pending)) {
-                        disk = ndisk;
-                        slot = nslot;
+                if (conf->near_copies > 1 && !atomic_read(&rdev->nr_pending))
                         break;
-                }
 
                 /* for far > 1 always use the lowest address */
                 if (conf->far_copies > 1)
-                        new_distance = r10_bio->devs[nslot].addr;
+                        new_distance = r10_bio->devs[slot].addr;
                 else
-                        new_distance = abs(r10_bio->devs[nslot].addr -
-                                           conf->mirrors[ndisk].head_position);
-                if (new_distance < current_distance) {
-                        current_distance = new_distance;
-                        disk = ndisk;
-                        slot = nslot;
+                        new_distance = abs(r10_bio->devs[slot].addr -
+                                           conf->mirrors[disk].head_position);
+                if (new_distance < best_dist) {
+                        best_dist = new_distance;
+                        best_slot = slot;
                 }
         }
+        if (slot == conf->copies)
+                slot = best_slot;
 
-rb_out:
-        r10_bio->read_slot = slot;
-/*      conf->next_seq_sect = this_sector + sectors;*/
-
-        if (disk >= 0 && (rdev=rcu_dereference(conf->mirrors[disk].rdev))!= NULL)
-                atomic_inc(&conf->mirrors[disk].rdev->nr_pending);
-        else
+        if (slot >= 0) {
+                disk = r10_bio->devs[slot].devnum;
+                rdev = rcu_dereference(conf->mirrors[disk].rdev);
+                if (!rdev)
+                        goto retry;
+                atomic_inc(&rdev->nr_pending);
+                if (test_bit(Faulty, &rdev->flags)) {
+                        /* Cannot risk returning a device that failed
+                         * before we inc'ed nr_pending
+                         */
+                        rdev_dec_pending(rdev, conf->mddev);
+                        goto retry;
+                }
+                r10_bio->read_slot = slot;
+        } else
                 disk = -1;
         rcu_read_unlock();