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md: simplify raid10 read_balance

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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>
This commit is contained in:
NeilBrown 2011-05-11 14:27:03 +10:00
parent 8258c53208
commit 56d9912106
1 changed files with 45 additions and 67 deletions
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112
drivers/md/raid10.c
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@ -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;
&& (this_sector + sectors >= conf->next_resync))
do_balance = 0;
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;
}
/* 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;
}
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))
for (slot = 0; slot < conf->copies ; slot++) {
if (r10_bio->devs[slot].bio == IO_BLOCKED)
continue;
disk = r10_bio->devs[slot].devnum;
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();