From 76073054c95b12af6bd0cc9b9462a265b45ba38f Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Wed, 11 May 2011 14:34:56 +1000 Subject: [PATCH] md/raid1: clean up read_balance. 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 --- drivers/md/raid1.c | 83 +++++++++++++++++++--------------------------- 1 file changed, 34 insertions(+), 49 deletions(-) diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c index 2b7a7ff401dc..f0b0c79b3899 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c @@ -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) -- 2.20.1