[PATCH] md: support write-mostly device in raid1
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>
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index ba643e4b..28839a8 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -360,13 +360,14 @@
{
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 @@
/* 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 @@
/* 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 @@
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 @@
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 @@
*/
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);