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[PATCH] md: support write-mostly device in raid1

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This allows a device in a raid1 to be marked as "write mostly".  Read requests
will only be sent if there is no other option.

Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
NeilBrown
2005-09-09 16:23:45 -07:00
committed by Linus Torvalds
parent 36fa30636f
commit 8ddf9efe67
4 changed files with 82 additions and 26 deletions
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76
drivers/md/raid1.c
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@@ -360,13 +360,14 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio)
{
const unsigned long this_sector = r1_bio->sector;
int new_disk = conf->last_used, disk = new_disk;
int wonly_disk = -1;
const int sectors = r1_bio->sectors;
sector_t new_distance, current_distance;
mdk_rdev_t *new_rdev, *rdev;
mdk_rdev_t *rdev;
rcu_read_lock();
/*
* Check if it if we can balance. We can balance on the whole
* Check if we can balance. We can balance on the whole
* device if no resync is going on, or below the resync window.
* We take the first readable disk when above the resync window.
*/
@@ -376,11 +377,16 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio)
/* Choose the first operation device, for consistancy */
new_disk = 0;
while ((new_rdev=conf->mirrors[new_disk].rdev) == NULL ||
!new_rdev->in_sync) {
new_disk++;
if (new_disk == conf->raid_disks) {
new_disk = -1;
for (rdev = conf->mirrors[new_disk].rdev;
!rdev || !rdev->in_sync
|| test_bit(WriteMostly, &rdev->flags);
rdev = conf->mirrors[++new_disk].rdev) {
if (rdev && rdev->in_sync)
wonly_disk = new_disk;
if (new_disk == conf->raid_disks - 1) {
new_disk = wonly_disk;
break;
}
}
@@ -389,16 +395,26 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio)
/* make sure the disk is operational */
while ((new_rdev=conf->mirrors[new_disk].rdev) == NULL ||
!new_rdev->in_sync) {
for (rdev = conf->mirrors[new_disk].rdev;
!rdev || !rdev->in_sync ||
test_bit(WriteMostly, &rdev->flags);
rdev = conf->mirrors[new_disk].rdev) {
if (rdev && rdev->in_sync)
wonly_disk = new_disk;
if (new_disk <= 0)
new_disk = conf->raid_disks;
new_disk--;
if (new_disk == disk) {
new_disk = -1;
goto rb_out;
new_disk = wonly_disk;
break;
}
}
if (new_disk < 0)
goto rb_out;
disk = new_disk;
/* now disk == new_disk == starting point for search */
@@ -419,37 +435,41 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio)
disk = conf->raid_disks;
disk--;
if ((rdev=conf->mirrors[disk].rdev) == NULL ||
!rdev->in_sync)
rdev = conf->mirrors[disk].rdev;
if (!rdev ||
!rdev->in_sync ||
test_bit(WriteMostly, &rdev->flags))
continue;
if (!atomic_read(&rdev->nr_pending)) {
new_disk = disk;
new_rdev = rdev;
break;
}
new_distance = abs(this_sector - conf->mirrors[disk].head_position);
if (new_distance < current_distance) {
current_distance = new_distance;
new_disk = disk;
new_rdev = rdev;
}
} while (disk != conf->last_used);
rb_out:
rb_out:
if (new_disk >= 0) {
conf->next_seq_sect = this_sector + sectors;
conf->last_used = new_disk;
atomic_inc(&new_rdev->nr_pending);
if (!new_rdev->in_sync) {
rdev = conf->mirrors[new_disk].rdev;
if (!rdev)
goto retry;
atomic_inc(&rdev->nr_pending);
if (!rdev->in_sync) {
/* cannot risk returning a device that failed
* before we inc'ed nr_pending
*/
atomic_dec(&new_rdev->nr_pending);
atomic_dec(&rdev->nr_pending);
goto retry;
}
conf->next_seq_sect = this_sector + sectors;
conf->last_used = new_disk;
}
rcu_read_unlock();
@@ -1109,6 +1129,7 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
sector_t max_sector, nr_sectors;
int disk;
int i;
int wonly;
int write_targets = 0;
int sync_blocks;
int still_degraded = 0;
@@ -1164,14 +1185,21 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
*/
disk = conf->last_used;
/* make sure disk is operational */
wonly = disk;
while (conf->mirrors[disk].rdev == NULL ||
!conf->mirrors[disk].rdev->in_sync) {
!conf->mirrors[disk].rdev->in_sync ||
test_bit(WriteMostly, &conf->mirrors[disk].rdev->flags)
) {
if (conf->mirrors[disk].rdev &&
conf->mirrors[disk].rdev->in_sync)
wonly = disk;
if (disk <= 0)
disk = conf->raid_disks;
disk--;
if (disk == conf->last_used)
if (disk == conf->last_used) {
disk = wonly;
break;
}
}
conf->last_used = disk;
atomic_inc(&conf->mirrors[disk].rdev->nr_pending);