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Subject[PATCH 030 of 35] Teach raid5 to split incoming bios.

We only need to split bios if we want to read around the cache,
as when we go through the cache, the sharing is already done.

So use bio_multi_split to split up read requests, and get rid of
raid5_mergeable_bvec as it is no longer needed.

Signed-off-by: Neil Brown <neilb@suse.de>

### Diffstat output
./drivers/md/raid5.c | 86 ++++++++++-----------------------------------------
1 file changed, 18 insertions(+), 68 deletions(-)
diff .prev/drivers/md/raid5.c ./drivers/md/raid5.c
--- .prev/drivers/md/raid5.c 2007-07-31 11:21:22.000000000 +1000
+++ ./drivers/md/raid5.c 2007-07-31 11:21:25.000000000 +1000
@@ -3805,39 +3805,6 @@ static int raid5_congested(void *data, i
return 0;
}

-/* We want read requests to align with chunks where possible,
- * but write requests don't need to.
- */
-static int raid5_mergeable_bvec(struct request_queue *q, struct bio *bio, struct bio_vec *biovec)
-{
- mddev_t *mddev = q->queuedata;
- sector_t sector = bio->bi_sector + get_start_sect(bio->bi_bdev);
- int max;
- unsigned int chunk_sectors = mddev->chunk_size >> 9;
- unsigned int bio_sectors = bio->bi_size >> 9;
-
- if (bio_data_dir(bio) == WRITE)
- return biovec->bv_len; /* always allow writes to be mergeable */
-
- max = (chunk_sectors - ((sector & (chunk_sectors - 1)) + bio_sectors)) << 9;
- if (max < 0) max = 0;
- if (max <= biovec->bv_len && bio_sectors == 0)
- return biovec->bv_len;
- else
- return max;
-}
-
-
-static int in_chunk_boundary(mddev_t *mddev, struct bio *bio)
-{
- sector_t sector = bio->bi_sector + get_start_sect(bio->bi_bdev);
- unsigned int chunk_sectors = mddev->chunk_size >> 9;
- unsigned int bio_sectors = bio->bi_size >> 9;
-
- return chunk_sectors >=
- ((sector & (chunk_sectors - 1)) + bio_sectors);
-}
-
/*
* add bio to the retry LIFO ( in O(1) ... we are in interrupt )
* later sampled by raid5d.
@@ -3914,23 +3881,6 @@ static void raid5_align_endio(struct bio
add_bio_to_retry(raid_bi, conf);
}

-static int bio_fits_rdev(struct bio *bi)
-{
- struct request_queue *q = bdev_get_queue(bi->bi_bdev);
-
- if ((bi->bi_size>>9) > q->max_sectors)
- return 0;
-
- if (q->merge_bvec_fn)
- /* it's too hard to apply the merge_bvec_fn at this stage,
- * just just give up
- */
- return 0;
-
- return 1;
-}
-
-
static int chunk_aligned_read(struct request_queue *q, struct bio * raid_bio)
{
mddev_t *mddev = q->queuedata;
@@ -3941,16 +3891,10 @@ static int chunk_aligned_read(struct req
struct bio* align_bi;
mdk_rdev_t *rdev;

- if (!in_chunk_boundary(mddev, raid_bio)) {
- pr_debug("chunk_aligned_read : non aligned\n");
- return 0;
- }
/*
* use bio_clone to make a copy of the bio
*/
align_bi = bio_clone(raid_bio, GFP_NOIO);
- if (!align_bi)
- return 0;
/*
* set bi_end_io to a new function, and set bi_private to the
* original bio.
@@ -3976,13 +3920,6 @@ static int chunk_aligned_read(struct req
align_bi->bi_bdev = rdev->bdev;
align_bi->bi_sector += rdev->data_offset;

- if (!bio_fits_rdev(align_bi)) {
- /* too big in some way */
- bio_put(align_bi);
- rdev_dec_pending(rdev, mddev);
- return 0;
- }
-
spin_lock_irq(&conf->device_lock);
wait_event_lock_irq(conf->wait_for_queue,
conf->quiesce == 0,
@@ -4021,9 +3958,24 @@ static int make_request(struct request_q
disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bi));

if (rw == READ &&
- mddev->reshape_position == MaxSector &&
- chunk_aligned_read(q,bi))
- return 0;
+ mddev->reshape_position == MaxSector) {
+ struct bio *remainder = bi;
+ int chunk_sects = mddev->chunk_size >> 9;
+ while (chunk_sects < ((remainder->bi_sector & (chunk_sects - 1))
+ + (remainder->bi_size >> 9))) {
+ struct bio *new =
+ bio_multi_split(bi,
+ chunk_sects -
+ (remainder->bi_sector
+ & (chunk_sects - 1)),
+ &remainder);
+ if (!chunk_aligned_read(q, new))
+ make_request(q, new);
+ }
+ bi = remainder;
+ if (chunk_aligned_read(q, bi))
+ return 0;
+ }

logical_sector = bi->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
last_sector = bi->bi_sector + (bi->bi_size>>9);
@@ -4948,8 +4900,6 @@ static int run(mddev_t *mddev)
mddev->array_size = mddev->size * (conf->previous_raid_disks -
conf->max_degraded);

- blk_queue_merge_bvec(mddev->queue, raid5_mergeable_bvec);
-
return 0;
abort:
if (conf) {
-
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