md/raid10: add failfast handling for reads.

If a device is marked FailFast, and it is not the only
device we can read from, we mark the bio as MD_FAILFAST.

If this does fail-fast, we don't try read repair but just
allow failure.

If it was the last device, it doesn't get marked Faulty so
the retry happens on the same device - this time without
FAILFAST.  A subsequent failure will not retry but will just
pass up the error.

During resync we may use FAILFAST requests, and on a failure
we will simply use the other device(s).

During recovery we will only use FAILFAST in the unusual
case were there are multiple places to read from - i.e. if
there are > 2 devices.  If we get a failure we will fail the
device and complete the resync/recovery with remaining
devices.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index af50866f5ffbd66c086076f1afc6f0e090b32daa..7cdc9bcd21b0f801f07eaa054c7e936074f500c8 100644 (file)
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -719,6 +719,7 @@ static struct md_rdev *read_balance(struct r10conf *conf,
        best_dist = MaxSector;
        best_good_sectors = 0;
        do_balance = 1;
+       clear_bit(R10BIO_FailFast, &r10_bio->state);
        /*
         * Check if we can balance. We can balance on the whole
         * device if no resync is going on (recovery is ok), or below
@@ -783,15 +784,18 @@ static struct md_rdev *read_balance(struct r10conf *conf,
                if (!do_balance)
                        break;
 
+               if (best_slot >= 0)
+                       /* At least 2 disks to choose from so failfast is OK */
+                       set_bit(R10BIO_FailFast, &r10_bio->state);
                /* This optimisation is debatable, and completely destroys
                 * sequential read speed for 'far copies' arrays.  So only
                 * keep it for 'near' arrays, and review those later.
                 */
                if (geo->near_copies > 1 && !atomic_read(&rdev->nr_pending))
-                       break;
+                       new_distance = 0;
 
                /* for far > 1 always use the lowest address */
-               if (geo->far_copies > 1)
+               else if (geo->far_copies > 1)
                        new_distance = r10_bio->devs[slot].addr;
                else
                        new_distance = abs(r10_bio->devs[slot].addr -
@@ -1170,6 +1174,9 @@ read_again:
                read_bio->bi_bdev = rdev->bdev;
                read_bio->bi_end_io = raid10_end_read_request;
                bio_set_op_attrs(read_bio, op, do_sync);
+               if (test_bit(FailFast, &rdev->flags) &&
+                   test_bit(R10BIO_FailFast, &r10_bio->state))
+                       read_bio->bi_opf |= MD_FAILFAST;
                read_bio->bi_private = r10_bio;
 
                if (mddev->gendisk)
@@ -1988,6 +1995,7 @@ static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
        /* now find blocks with errors */
        for (i=0 ; i < conf->copies ; i++) {
                int  j, d;
+               struct md_rdev *rdev;
 
                tbio = r10_bio->devs[i].bio;
 
@@ -1995,6 +2003,8 @@ static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
                        continue;
                if (i == first)
                        continue;
+               d = r10_bio->devs[i].devnum;
+               rdev = conf->mirrors[d].rdev;
                if (!r10_bio->devs[i].bio->bi_error) {
                        /* We know that the bi_io_vec layout is the same for
                         * both 'first' and 'i', so we just compare them.
@@ -2017,6 +2027,10 @@ static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
                        if (test_bit(MD_RECOVERY_CHECK, &mddev->recovery))
                                /* Don't fix anything. */
                                continue;
+               } else if (test_bit(FailFast, &rdev->flags)) {
+                       /* Just give up on this device */
+                       md_error(rdev->mddev, rdev);
+                       continue;
                }
                /* Ok, we need to write this bio, either to correct an
                 * inconsistency or to correct an unreadable block.
@@ -2034,7 +2048,6 @@ static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
 
                bio_copy_data(tbio, fbio);
 
-               d = r10_bio->devs[i].devnum;
                atomic_inc(&conf->mirrors[d].rdev->nr_pending);
                atomic_inc(&r10_bio->remaining);
                md_sync_acct(conf->mirrors[d].rdev->bdev, bio_sectors(tbio));
@@ -2541,12 +2554,14 @@ static void handle_read_error(struct mddev *mddev, struct r10bio *r10_bio)
        bio_put(bio);
        r10_bio->devs[slot].bio = NULL;
 
-       if (mddev->ro == 0) {
+       if (mddev->ro)
+               r10_bio->devs[slot].bio = IO_BLOCKED;
+       else if (!test_bit(FailFast, &rdev->flags)) {
                freeze_array(conf, 1);
                fix_read_error(conf, mddev, r10_bio);
                unfreeze_array(conf);
        } else
-               r10_bio->devs[slot].bio = IO_BLOCKED;
+               md_error(mddev, rdev);
 
        rdev_dec_pending(rdev, mddev);
 
@@ -2575,6 +2590,9 @@ read_more:
                + choose_data_offset(r10_bio, rdev);
        bio->bi_bdev = rdev->bdev;
        bio_set_op_attrs(bio, REQ_OP_READ, do_sync);
+       if (test_bit(FailFast, &rdev->flags) &&
+           test_bit(R10BIO_FailFast, &r10_bio->state))
+               bio->bi_opf |= MD_FAILFAST;
        bio->bi_private = r10_bio;
        bio->bi_end_io = raid10_end_read_request;
        trace_block_bio_remap(bdev_get_queue(bio->bi_bdev),
@@ -3096,6 +3114,8 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
                                bio->bi_private = r10_bio;
                                bio->bi_end_io = end_sync_read;
                                bio_set_op_attrs(bio, REQ_OP_READ, 0);
+                               if (test_bit(FailFast, &rdev->flags))
+                                       bio->bi_opf |= MD_FAILFAST;
                                from_addr = r10_bio->devs[j].addr;
                                bio->bi_iter.bi_sector = from_addr +
                                        rdev->data_offset;
@@ -3201,6 +3221,23 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
                        rdev_dec_pending(mrdev, mddev);
                        if (mreplace)
                                rdev_dec_pending(mreplace, mddev);
+                       if (r10_bio->devs[0].bio->bi_opf & MD_FAILFAST) {
+                               /* Only want this if there is elsewhere to
+                                * read from. 'j' is currently the first
+                                * readable copy.
+                                */
+                               int targets = 1;
+                               for (; j < conf->copies; j++) {
+                                       int d = r10_bio->devs[j].devnum;
+                                       if (conf->mirrors[d].rdev &&
+                                           test_bit(In_sync,
+                                                     &conf->mirrors[d].rdev->flags))
+                                               targets++;
+                               }
+                               if (targets == 1)
+                                       r10_bio->devs[0].bio->bi_opf
+                                               &= ~MD_FAILFAST;
+                       }
                }
                if (biolist == NULL) {
                        while (r10_bio) {
@@ -3279,6 +3316,8 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
                        bio->bi_private = r10_bio;
                        bio->bi_end_io = end_sync_read;
                        bio_set_op_attrs(bio, REQ_OP_READ, 0);
+                       if (test_bit(FailFast, &conf->mirrors[d].rdev->flags))
+                               bio->bi_opf |= MD_FAILFAST;
                        bio->bi_iter.bi_sector = sector + rdev->data_offset;
                        bio->bi_bdev = rdev->bdev;
                        count++;

diff --git a/drivers/md/raid10.h b/drivers/md/raid10.h
index 18ec1f7a98bf77c98da88eaaa7ff0a95da2ac30a..3162615e57bd581a9125e3135eb01e80dfed93a0 100644 (file)
--- a/drivers/md/raid10.h
+++ b/drivers/md/raid10.h
@@ -156,5 +156,7 @@ enum r10bio_state {
  * flag is set
  */
        R10BIO_Previous,
+/* failfast devices did receive failfast requests. */
+       R10BIO_FailFast,
 };
 #endif