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md/raid10: preferentially read from replacement device if possible.

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When reading (for array reads, not for recovery etc) we read from the
replacement device if it has recovered far enough.
This requires storing the chosen rdev in the 'r10_bio' so we can make
sure to drop the ref on the right device when the read finishes.

Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
NeilBrown 2011-12-23 10:17:54 +11:00
parent 96c3fd1f38
commit abbf098e6e
1 changed files with 23 additions and 13 deletions
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36
drivers/md/raid10.c
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@ -324,11 +324,13 @@ static void raid10_end_read_request(struct bio *bio, int error)
int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
struct r10bio *r10_bio = bio->bi_private;
int slot, dev;
struct md_rdev *rdev;
struct r10conf *conf = r10_bio->mddev->private;
slot = r10_bio->read_slot;
dev = r10_bio->devs[slot].devnum;
rdev = r10_bio->devs[slot].rdev;
/*
* this branch is our 'one mirror IO has finished' event handler:
*/
@ -346,7 +348,7 @@ static void raid10_end_read_request(struct bio *bio, int error)
*/
set_bit(R10BIO_Uptodate, &r10_bio->state);
raid_end_bio_io(r10_bio);
rdev_dec_pending(conf->mirrors[dev].rdev, conf->mddev);
rdev_dec_pending(rdev, conf->mddev);
} else {
/*
* oops, read error - keep the refcount on the rdev
@ -355,7 +357,7 @@ static void raid10_end_read_request(struct bio *bio, int error)
printk_ratelimited(KERN_ERR
"md/raid10:%s: %s: rescheduling sector %llu\n",
mdname(conf->mddev),
bdevname(conf->mirrors[dev].rdev->bdev, b),
bdevname(rdev->bdev, b),
(unsigned long long)r10_bio->sector);
set_bit(R10BIO_ReadError, &r10_bio->state);
reschedule_retry(r10_bio);
@ -599,7 +601,7 @@ static struct md_rdev *read_balance(struct r10conf *conf,
int sectors = r10_bio->sectors;
int best_good_sectors;
sector_t new_distance, best_dist;
struct md_rdev *rdev;
struct md_rdev *rdev, *best_rdev;
int do_balance;
int best_slot;
@ -608,6 +610,7 @@ static struct md_rdev *read_balance(struct r10conf *conf,
retry:
sectors = r10_bio->sectors;
best_slot = -1;
best_rdev = NULL;
best_dist = MaxSector;
best_good_sectors = 0;
do_balance = 1;
@ -629,10 +632,16 @@ retry:
if (r10_bio->devs[slot].bio == IO_BLOCKED)
continue;
disk = r10_bio->devs[slot].devnum;
rdev = rcu_dereference(conf->mirrors[disk].rdev);
rdev = rcu_dereference(conf->mirrors[disk].replacement);
if (rdev == NULL || test_bit(Faulty, &rdev->flags) ||
r10_bio->devs[slot].addr + sectors > rdev->recovery_offset)
rdev = rcu_dereference(conf->mirrors[disk].rdev);
if (rdev == NULL)
continue;
if (!test_bit(In_sync, &rdev->flags))
if (test_bit(Faulty, &rdev->flags))
continue;
if (!test_bit(In_sync, &rdev->flags) &&
r10_bio->devs[slot].addr + sectors > rdev->recovery_offset)
continue;
dev_sector = r10_bio->devs[slot].addr;
@ -657,6 +666,7 @@ retry:
if (good_sectors > best_good_sectors) {
best_good_sectors = good_sectors;
best_slot = slot;
best_rdev = rdev;
}
if (!do_balance)
/* Must read from here */
@ -685,16 +695,15 @@ retry:
if (new_distance < best_dist) {
best_dist = new_distance;
best_slot = slot;
best_rdev = rdev;
}
}
if (slot == conf->copies)
if (slot >= conf->copies) {
slot = best_slot;
rdev = best_rdev;
}
if (slot >= 0) {
disk = r10_bio->devs[slot].devnum;
rdev = rcu_dereference(conf->mirrors[disk].rdev);
if (!rdev)
goto retry;
atomic_inc(&rdev->nr_pending);
if (test_bit(Faulty, &rdev->flags)) {
/* Cannot risk returning a device that failed
@ -990,6 +999,7 @@ read_again:
max_sectors);
r10_bio->devs[slot].bio = read_bio;
r10_bio->devs[slot].rdev = rdev;
read_bio->bi_sector = r10_bio->devs[slot].addr +
rdev->data_offset;
@ -2088,10 +2098,9 @@ static int narrow_write_error(struct r10bio *r10_bio, int i)
static void handle_read_error(struct mddev *mddev, struct r10bio *r10_bio)
{
int slot = r10_bio->read_slot;
int mirror = r10_bio->devs[slot].devnum;
struct bio *bio;
struct r10conf *conf = mddev->private;
struct md_rdev *rdev;
struct md_rdev *rdev = r10_bio->devs[slot].rdev;
char b[BDEVNAME_SIZE];
unsigned long do_sync;
int max_sectors;
@ -2109,7 +2118,7 @@ static void handle_read_error(struct mddev *mddev, struct r10bio *r10_bio)
fix_read_error(conf, mddev, r10_bio);
unfreeze_array(conf);
}
rdev_dec_pending(conf->mirrors[mirror].rdev, mddev);
rdev_dec_pending(rdev, mddev);
bio = r10_bio->devs[slot].bio;
bdevname(bio->bi_bdev, b);
@ -2144,6 +2153,7 @@ read_more:
r10_bio->sector - bio->bi_sector,
max_sectors);
r10_bio->devs[slot].bio = bio;
r10_bio->devs[slot].rdev = rdev;
bio->bi_sector = r10_bio->devs[slot].addr
+ rdev->data_offset;
bio->bi_bdev = rdev->bdev;