[PATCH RFC 3/3] improve raid10 discard request

[Xiao Ni <xni@redhat.com>]

Now the discard request is split by chunk size. So it takes a long time to finish mkfs on
disks which support discard function. This patch improve handling raid10 discard request.
It uses  the similar way with raid0(29efc390b).

But it's a little complex than raid0. Because raid10 has different layout. If raid10 is
offset layout and the discard request is smaller than stripe size. There are some holes
when we submit discard bio to underlayer disks.

For example: five disks (disk1 - disk5)
D01 D02 D03 D04 D05
D05 D01 D02 D03 D04
D06 D07 D08 D09 D10
D10 D06 D07 D08 D09
The discard bio just wants to discard from D03 to D10. For disk3, there is a hole between
D03 and D08. For disk4, there is a hole between D04 and D09. D03 is a chunk, raid10_write_request
can handle one chunk perfectly. So the part that is not aligned with stripe size is still
handled by raid10_write_request.

If reshape is running when discard bio comes and the discard bio spans the reshape position,
raid10_write_request is responsible to handle this discard bio.

I did a test with this patch set.
Without patch:
time mkfs.xfs /dev/md0
real4m39.775s
user0m0.000s
sys0m0.298s

With patch:
time mkfs.xfs /dev/md0
real0m0.105s
user0m0.000s
sys0m0.007s

nvme3n1           259:1    0   477G  0 disk
└─nvme3n1p1       259:10   0    50G  0 part
nvme4n1           259:2    0   477G  0 disk
└─nvme4n1p1       259:11   0    50G  0 part
nvme5n1           259:6    0   477G  0 disk
└─nvme5n1p1       259:12   0    50G  0 part
nvme2n1           259:9    0   477G  0 disk
└─nvme2n1p1       259:15   0    50G  0 part
nvme0n1           259:13   0   477G  0 disk
└─nvme0n1p1       259:14   0    50G  0 part

Signed-off-by: Xiao Ni <xni@redhat.com>
---
 drivers/md/raid10.c | 266 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 265 insertions(+), 1 deletion(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 2a7423e..417a1ff 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1518,6 +1518,261 @@ static void __make_request(struct mddev *mddev, struct bio *bio, int sectors)
 		raid10_write_request(mddev, bio, r10_bio);
 }
 
+static void wait_blocked_dev(struct mddev *mddev, int cnt)
+{
+	int i;
+	struct r10conf *conf = mddev->private;
+	struct md_rdev *blocked_rdev = NULL;
+
+retry_wait:
+	rcu_read_lock();
+	for (i = 0; i < cnt; i++) {
+		struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
+		struct md_rdev *rrdev = rcu_dereference(
+			conf->mirrors[i].replacement);
+		if (rdev == rrdev)
+			rrdev = NULL;
+		if (rdev && unlikely(test_bit(Blocked, &rdev->flags))) {
+			atomic_inc(&rdev->nr_pending);
+			blocked_rdev = rdev;
+			break;
+		}
+		if (rrdev && unlikely(test_bit(Blocked, &rrdev->flags))) {
+			atomic_inc(&rrdev->nr_pending);
+			blocked_rdev = rrdev;
+			break;
+		}
+	}
+	rcu_read_unlock();
+
+	if (unlikely(blocked_rdev)) {
+		/* Have to wait for this device to get unblocked, then retry */
+		allow_barrier(conf);
+		raid10_log(conf->mddev, "%s wait rdev %d blocked", __func__, blocked_rdev->raid_disk);
+		md_wait_for_blocked_rdev(blocked_rdev, mddev);
+		wait_barrier(conf);
+		goto retry_wait;
+	}
+}
+
+static struct bio *raid10_split_bio(struct r10conf *conf,
+			struct bio *bio, int sectors, bool want_first)
+{
+	struct bio *split;
+
+	split = bio_split(bio, sectors,	GFP_NOIO, &conf->bio_split);
+	bio_chain(split, bio);
+	allow_barrier(conf);
+	if (want_first) {
+		submit_bio_noacct(bio);
+		bio = split;
+	} else
+		submit_bio_noacct(split);
+	wait_barrier(conf);
+
+	return bio;
+}
+
+static void raid10_end_discard_request(struct bio *bio)
+{
+	struct r10bio *r10_bio = bio->bi_private;
+        struct r10conf *conf = r10_bio->mddev->private;
+	struct md_rdev *rdev = NULL;
+        int dev;
+        int slot, repl;
+
+	/*
+	 * We don't care the return value of discard bio
+	 */
+	set_bit(R10BIO_Uptodate, &r10_bio->state);
+
+	dev = find_bio_disk(conf, r10_bio, bio, &slot, &repl);
+	if (repl)
+		rdev = conf->mirrors[dev].replacement;
+	if (!rdev) {
+		smp_rmb();
+		repl = 0;
+		rdev = conf->mirrors[dev].rdev;
+	}
+
+	if (atomic_dec_and_test(&r10_bio->remaining)) {
+		md_write_end(r10_bio->mddev);
+		raid_end_bio_io(r10_bio);
+	}
+
+	rdev_dec_pending(rdev, conf->mddev);
+}
+
+static bool raid10_handle_discard(struct mddev *mddev, struct bio *bio)
+{
+	struct r10conf *conf = mddev->private;
+	struct geom geo = conf->geo;
+	struct r10bio *r10_bio;
+
+	int disk;
+	sector_t chunk;
+	int stripe_size, stripe_mask;
+
+	sector_t bio_start, bio_end;
+	sector_t first_stripe_index, last_stripe_index;
+	sector_t start_disk_offset;
+	unsigned int start_disk_index;
+	sector_t end_disk_offset;
+	unsigned int end_disk_index;
+
+	wait_barrier(conf);
+
+	if (conf->reshape_progress != MaxSector &&
+	    ((bio->bi_iter.bi_sector >= conf->reshape_progress) !=
+	     conf->mddev->reshape_backwards))
+		geo = conf->prev;
+
+	stripe_size = (1<<geo.chunk_shift) * geo.raid_disks;
+	stripe_mask = stripe_size - 1;
+
+	if (bio_sectors(bio) < stripe_size)
+		goto out;
+
+	if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
+	     bio->bi_iter.bi_sector < conf->reshape_progress &&
+	     bio->bi_iter.bi_sector + bio_sectors(bio) > conf->reshape_progress)
+		goto out;
+
+	r10_bio = mempool_alloc(&conf->r10bio_pool, GFP_NOIO);
+	r10_bio->mddev = mddev;
+	r10_bio->state = 0;
+	memset(r10_bio->devs, 0, sizeof(r10_bio->devs[0]) * conf->geo.raid_disks);
+
+	wait_blocked_dev(mddev, geo.raid_disks);
+
+	/* For far offset layout, if bio is not aligned with stripe size, it splits
+	 * the part that is not aligned with strip size.
+	 */
+
+	bio_start = bio->bi_iter.bi_sector;
+	bio_end = bio_end_sector(bio);
+	if (geo.far_offset && (bio_start & stripe_mask)) {
+		sector_t split_size;
+		split_size = round_up(bio_start, stripe_size) - bio_start;
+		bio = raid10_split_bio(conf, bio, split_size, false);
+	}
+	if (geo.far_offset && ((bio_end & stripe_mask) != stripe_mask)) {
+		sector_t split_size;
+		split_size = bio_end - (bio_end & stripe_mask);
+		bio = raid10_split_bio(conf, bio, split_size, true);
+	}
+	r10_bio->master_bio = bio;
+
+	bio_start = bio->bi_iter.bi_sector;
+	bio_end = bio_end_sector(bio);
+
+	chunk = bio_start >> geo.chunk_shift;
+	chunk *= geo.near_copies;
+	first_stripe_index = chunk;
+	start_disk_index = sector_div(first_stripe_index, geo.raid_disks);
+	if (geo.far_offset)
+		first_stripe_index *= geo.far_copies;
+	start_disk_offset = (bio_start & geo.chunk_mask) +
+				(first_stripe_index << geo.chunk_shift);
+
+	chunk = bio_end >> geo.chunk_shift;
+	chunk *= geo.near_copies;
+	last_stripe_index = chunk;
+	end_disk_index = sector_div(last_stripe_index, geo.raid_disks);
+	if (geo.far_offset)
+		last_stripe_index *= geo.far_copies;
+	end_disk_offset = (bio_end & geo.chunk_mask) +
+				(last_stripe_index << geo.chunk_shift);
+
+	rcu_read_lock();
+	for (disk = 0; disk < geo.raid_disks; disk++) {
+		struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev);
+		struct md_rdev *rrdev = rcu_dereference(
+			conf->mirrors[disk].replacement);
+
+		r10_bio->devs[disk].bio = NULL;
+		r10_bio->devs[disk].repl_bio = NULL;
+
+		if (rdev && (test_bit(Faulty, &rdev->flags)))
+			rdev = NULL;
+		if (rrdev && (test_bit(Faulty, &rrdev->flags)))
+			rrdev = NULL;
+		if (!rdev && !rrdev)
+			continue;
+
+		if (rdev) {
+			r10_bio->devs[disk].bio = bio;
+			atomic_inc(&rdev->nr_pending);
+		}
+		if (rrdev) {
+			r10_bio->devs[disk].repl_bio = bio;
+			atomic_inc(&rrdev->nr_pending);
+		}
+	}
+	rcu_read_unlock();
+
+	atomic_set(&r10_bio->remaining, 1);
+	for (disk = 0; disk < geo.raid_disks; disk++) {
+		sector_t dev_start, dev_end;
+		struct bio *mbio, *rbio = NULL;
+		struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev);
+		struct md_rdev *rrdev = rcu_dereference(
+			conf->mirrors[disk].replacement);
+
+		/*
+		 * Now start to calculate the start and end address for each disk.
+		 * The space between start and end is the discard region.
+		 */
+		if (disk < start_disk_index)
+			dev_start = (first_stripe_index + 1) * mddev->chunk_sectors;
+		else if (disk > start_disk_index)
+			dev_start = first_stripe_index * mddev->chunk_sectors;
+		else
+			dev_start = start_disk_offset;
+
+		if (disk < end_disk_index)
+			dev_end = (last_stripe_index + 1) * mddev->chunk_sectors;
+		else if (disk > end_disk_index)
+			dev_end = last_stripe_index * mddev->chunk_sectors;
+		else
+			dev_end = end_disk_offset;
+
+		/* It only handles discard bio which size is >= stripe size, so
+		 * dev_end > dev_start all the time
+		 */
+		if (r10_bio->devs[disk].bio) {
+			mbio = bio_clone_fast(bio, GFP_NOIO, &mddev->bio_set);
+			mbio->bi_end_io = raid10_end_discard_request;
+			mbio->bi_private = r10_bio;
+			r10_bio->devs[disk].bio = mbio;
+			r10_bio->devs[disk].devnum = disk;
+			atomic_inc(&r10_bio->remaining);
+			md_submit_discard_bio(mddev, rdev, mbio, dev_start, dev_end);
+			bio_endio(mbio);
+		}
+		if (r10_bio->devs[disk].repl_bio) {
+			rbio = bio_clone_fast(bio, GFP_NOIO, &mddev->bio_set);
+			rbio->bi_end_io = raid10_end_discard_request;
+			rbio->bi_private = r10_bio;
+			r10_bio->devs[disk].repl_bio = rbio;
+			r10_bio->devs[disk].devnum = disk;
+			atomic_inc(&r10_bio->remaining);
+			md_submit_discard_bio(mddev, rrdev, rbio, dev_start, dev_end);
+			bio_endio(rbio);
+		}
+	}
+
+	if (atomic_dec_and_test(&r10_bio->remaining)) {
+		md_write_end(r10_bio->mddev);
+		raid_end_bio_io(r10_bio);
+	}
+
+	return 0;
+out:
+	allow_barrier(conf);
+	return -EAGAIN;
+}
+
 static bool raid10_make_request(struct mddev *mddev, struct bio *bio)
 {
 	struct r10conf *conf = mddev->private;
@@ -1532,6 +1787,15 @@ static bool raid10_make_request(struct mddev *mddev, struct bio *bio)
 	if (!md_write_start(mddev, bio))
 		return false;
 
+	/* There are some limitations to handle discard bio
+	 * 1st, the discard size is bigger than stripe size.
+	 * 2st, if the discard bio spans reshape progress, we use the old way to
+	 * handle discard bio
+	 */
+	if (unlikely(bio_op(bio) == REQ_OP_DISCARD))
+		if (!raid10_handle_discard(mddev, bio))
+			return true;
+
 	/*
 	 * If this request crosses a chunk boundary, we need to split
 	 * it.
@@ -3762,7 +4026,7 @@ static int raid10_run(struct mddev *mddev)
 	chunk_size = mddev->chunk_sectors << 9;
 	if (mddev->queue) {
 		blk_queue_max_discard_sectors(mddev->queue,
-					      mddev->chunk_sectors);
+					      UINT_MAX);
 		blk_queue_max_write_same_sectors(mddev->queue, 0);
 		blk_queue_max_write_zeroes_sectors(mddev->queue, 0);
 		blk_queue_io_min(mddev->queue, chunk_size);
-- 
2.7.5