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md: tidy up device searches in read_balance.

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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>
This commit is contained in:
NeilBrown 2010-09-06 14:10:08 +10:00
parent 046abeede7
commit f3ac8bf7ce
1 changed files with 34 additions and 54 deletions
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88
drivers/md/raid1.c
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@ -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;
choose_first = 1;
start_disk = 0;
} else {
choose_first = 0;
start_disk = conf->last_used;
}
}
goto rb_out;
}
/* 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 @@ 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)