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md/raid1: clean up read_balance.

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read_balance has two loops which both look for a 'best'
device based on slightly different criteria.
This is clumsy and makes is hard to add extra criteria.

So replace it all with a single loop that combines everything.

Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
NeilBrown 2011-05-11 14:34:56 +10:00
parent 56d9912106
commit 76073054c9
1 changed files with 34 additions and 49 deletions
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83
drivers/md/raid1.c
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@ -411,10 +411,10 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio)
{
const sector_t this_sector = r1_bio->sector;
const int sectors = r1_bio->sectors;
int new_disk = -1;
int start_disk;
int best_disk;
int i;
sector_t new_distance, current_distance;
sector_t best_dist;
mdk_rdev_t *rdev;
int choose_first;
@ -425,6 +425,8 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio)
* We take the first readable disk when above the resync window.
*/
retry:
best_disk = -1;
best_dist = MaxSector;
if (conf->mddev->recovery_cp < MaxSector &&
(this_sector + sectors >= conf->next_resync)) {
choose_first = 1;
@ -434,8 +436,8 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio)
start_disk = conf->last_used;
}
/* make sure the disk is operational */
for (i = 0 ; i < conf->raid_disks ; i++) {
sector_t dist;
int disk = start_disk + i;
if (disk >= conf->raid_disks)
disk -= conf->raid_disks;
@ -443,60 +445,43 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio)
rdev = rcu_dereference(conf->mirrors[disk].rdev);
if (r1_bio->bios[disk] == IO_BLOCKED
|| rdev == NULL
|| !test_bit(In_sync, &rdev->flags))
|| test_bit(Faulty, &rdev->flags))
continue;
new_disk = disk;
if (!test_bit(WriteMostly, &rdev->flags))
break;
}
if (new_disk < 0 || choose_first)
goto rb_out;
/*
* Don't change to another disk for sequential reads:
*/
if (conf->next_seq_sect == this_sector)
goto rb_out;
if (this_sector == conf->mirrors[new_disk].head_position)
goto rb_out;
current_distance = abs(this_sector
- conf->mirrors[new_disk].head_position);
/* 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 (r1_bio->bios[disk] == IO_BLOCKED
|| rdev == NULL
|| !test_bit(In_sync, &rdev->flags)
|| test_bit(WriteMostly, &rdev->flags))
if (!test_bit(In_sync, &rdev->flags) &&
rdev->recovery_offset < this_sector + sectors)
continue;
if (!atomic_read(&rdev->nr_pending)) {
new_disk = disk;
if (test_bit(WriteMostly, &rdev->flags)) {
/* Don't balance among write-mostly, just
* use the first as a last resort */
if (best_disk < 0)
best_disk = disk;
continue;
}
/* This is a reasonable device to use. It might
* even be best.
*/
dist = abs(this_sector - conf->mirrors[disk].head_position);
if (choose_first
/* Don't change to another disk for sequential reads */
|| conf->next_seq_sect == this_sector
|| dist == 0
/* If device is idle, use it */
|| atomic_read(&rdev->nr_pending) == 0) {
best_disk = disk;
break;
}
new_distance = abs(this_sector - conf->mirrors[disk].head_position);
if (new_distance < current_distance) {
current_distance = new_distance;
new_disk = disk;
if (dist < best_dist) {
best_dist = dist;
best_disk = disk;
}
}
rb_out:
if (new_disk >= 0) {
rdev = rcu_dereference(conf->mirrors[new_disk].rdev);
if (best_disk >= 0) {
rdev = rcu_dereference(conf->mirrors[best_disk].rdev);
if (!rdev)
goto retry;
atomic_inc(&rdev->nr_pending);
if (!test_bit(In_sync, &rdev->flags)) {
if (test_bit(Faulty, &rdev->flags)) {
/* cannot risk returning a device that failed
* before we inc'ed nr_pending
*/
@ -504,11 +489,11 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio)
goto retry;
}
conf->next_seq_sect = this_sector + sectors;
conf->last_used = new_disk;
conf->last_used = best_disk;
}
rcu_read_unlock();
return new_disk;
return best_disk;
}
static int raid1_congested(void *data, int bits)