From f3ac8bf7ce1c5abd763ea762e95d1cdcf7799372 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Mon, 6 Sep 2010 14:10:08 +1000 Subject: [PATCH] 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 --- drivers/md/raid1.c | 92 ++++++++++++++++++---------------------------- 1 file changed, 36 insertions(+), 56 deletions(-) diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c index a0322db4d355..45f8324196ec 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c @@ -419,11 +419,13 @@ static void raid1_end_write_request(struct bio *bio, int error) 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 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) 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)) { - - if (rdev && test_bit(In_sync, &rdev->flags) && - r1_bio->bios[new_disk] != IO_BLOCKED) - wonly_disk = new_disk; - - if (new_disk <= 0) - new_disk = conf->raid_disks; - new_disk--; - if (new_disk == disk) { - new_disk = wonly_disk; + for (i = 0 ; i < conf->raid_disks ; i++) { + int disk = start_disk + i; + 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)) + continue; + + 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 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) 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 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) 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) -- 2.39.2