md: tidy up device searches in read_balance.
The code for searching through the device list to read-balance in
raid1 is rather clumsy and hard to follow. Try to simplify it a bit.
No important functionality change here.
Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index a0322db..45f8324 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -419,11 +419,13 @@
static int read_balance(conf_t *conf, r1bio_t *r1_bio)
{
const sector_t this_sector = r1_bio->sector;
- int new_disk = conf->last_used, disk = new_disk;
- int wonly_disk = -1;
const int sectors = r1_bio->sectors;
+ int new_disk = -1;
+ int start_disk;
+ int i;
sector_t new_distance, current_distance;
mdk_rdev_t *rdev;
+ int choose_first;
rcu_read_lock();
/*
@@ -434,54 +436,33 @@
retry:
if (conf->mddev->recovery_cp < MaxSector &&
(this_sector + sectors >= conf->next_resync)) {
- /* Choose the first operational device, for consistancy */
- new_disk = 0;
-
- for (rdev = rcu_dereference(conf->mirrors[new_disk].rdev);
- r1_bio->bios[new_disk] == IO_BLOCKED ||
- !rdev || !test_bit(In_sync, &rdev->flags)
- || test_bit(WriteMostly, &rdev->flags);
- rdev = rcu_dereference(conf->mirrors[++new_disk].rdev)) {
-
- if (rdev && test_bit(In_sync, &rdev->flags) &&
- r1_bio->bios[new_disk] != IO_BLOCKED)
- wonly_disk = new_disk;
-
- if (new_disk == conf->raid_disks - 1) {
- new_disk = wonly_disk;
- break;
- }
- }
- goto rb_out;
+ choose_first = 1;
+ start_disk = 0;
+ } else {
+ choose_first = 0;
+ start_disk = conf->last_used;
}
-
/* make sure the disk is operational */
- for (rdev = rcu_dereference(conf->mirrors[new_disk].rdev);
- r1_bio->bios[new_disk] == IO_BLOCKED ||
- !rdev || !test_bit(In_sync, &rdev->flags) ||
- test_bit(WriteMostly, &rdev->flags);
- rdev = rcu_dereference(conf->mirrors[new_disk].rdev)) {
+ for (i = 0 ; i < conf->raid_disks ; i++) {
+ int disk = start_disk + i;
+ if (disk >= conf->raid_disks)
+ disk -= conf->raid_disks;
- if (rdev && test_bit(In_sync, &rdev->flags) &&
- r1_bio->bios[new_disk] != IO_BLOCKED)
- wonly_disk = new_disk;
+ rdev = rcu_dereference(conf->mirrors[disk].rdev);
+ if (r1_bio->bios[disk] == IO_BLOCKED
+ || rdev == NULL
+ || !test_bit(In_sync, &rdev->flags))
+ continue;
- if (new_disk <= 0)
- new_disk = conf->raid_disks;
- new_disk--;
- if (new_disk == disk) {
- new_disk = wonly_disk;
+ new_disk = disk;
+ if (!test_bit(WriteMostly, &rdev->flags))
break;
- }
}
- if (new_disk < 0)
+ if (new_disk < 0 || choose_first)
goto rb_out;
- disk = new_disk;
- /* now disk == new_disk == starting point for search */
-
/*
* Don't change to another disk for sequential reads:
*/
@@ -490,20 +471,21 @@
if (this_sector == conf->mirrors[new_disk].head_position)
goto rb_out;
- current_distance = abs(this_sector - conf->mirrors[disk].head_position);
+ current_distance = abs(this_sector
+ - conf->mirrors[new_disk].head_position);
- /* Find the disk whose head is closest */
-
- do {
- if (disk <= 0)
- disk = conf->raid_disks;
- disk--;
+ /* look for a better disk - i.e. head is closer */
+ start_disk = new_disk;
+ for (i = 1; i < conf->raid_disks; i++) {
+ int disk = start_disk + 1;
+ if (disk >= conf->raid_disks)
+ disk -= conf->raid_disks;
rdev = rcu_dereference(conf->mirrors[disk].rdev);
-
- if (!rdev || r1_bio->bios[disk] == IO_BLOCKED ||
- !test_bit(In_sync, &rdev->flags) ||
- test_bit(WriteMostly, &rdev->flags))
+ if (r1_bio->bios[disk] == IO_BLOCKED
+ || rdev == NULL
+ || !test_bit(In_sync, &rdev->flags)
+ || test_bit(WriteMostly, &rdev->flags))
continue;
if (!atomic_read(&rdev->nr_pending)) {
@@ -515,11 +497,9 @@
current_distance = new_distance;
new_disk = disk;
}
- } while (disk != conf->last_used);
+ }
rb_out:
-
-
if (new_disk >= 0) {
rdev = rcu_dereference(conf->mirrors[new_disk].rdev);
if (!rdev)
