Commit ba58f57f authored by Yu Kuai's avatar Yu Kuai Committed by Song Liu
Browse files

md/raid1: factor out the code to manage sequential IO 



There is no functional change for now, make read_balance() cleaner and
prepare to fix problems and refactor the handler of sequential IO.

Co-developed-by: default avatarPaul Luse <paul.e.luse@linux.intel.com>
Signed-off-by: default avatarPaul Luse <paul.e.luse@linux.intel.com>
Signed-off-by: default avatarYu Kuai <yukuai3@huawei.com>
Reviewed-by: default avatarXiao Ni <xni@redhat.com>
Signed-off-by: default avatarSong Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20240229095714.926789-11-yukuai1@huaweicloud.com
parent 9f3ced79

drivers/md/raid1.c

+37 −34
Original line number Diff line number Diff line
@@ -705,6 +705,31 @@ static int choose_slow_rdev(struct r1conf *conf, struct r1bio *r1_bio, 
	return bb_disk;

}



static bool is_sequential(struct r1conf *conf, int disk, struct r1bio *r1_bio)

{

	/* TODO: address issues with this check and concurrency. */

	return conf->mirrors[disk].next_seq_sect == r1_bio->sector ||

	       conf->mirrors[disk].head_position == r1_bio->sector;

}



/*

 * If buffered sequential IO size exceeds optimal iosize, check if there is idle

 * disk. If yes, choose the idle disk.

 */

static bool should_choose_next(struct r1conf *conf, int disk)

{

	struct raid1_info *mirror = &conf->mirrors[disk];

	int opt_iosize;



	if (!test_bit(Nonrot, &mirror->rdev->flags))

		return false;



	opt_iosize = bdev_io_opt(mirror->rdev->bdev) >> 9;

	return opt_iosize > 0 && mirror->seq_start != MaxSector &&

	       mirror->next_seq_sect > opt_iosize &&

	       mirror->next_seq_sect - opt_iosize >= mirror->seq_start;

}



/*

 * This routine returns the disk from which the requested read should

 * be done. There is a per-array 'next expected sequential IO' sector
@@ -768,29 +793,11 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect 
		pending = atomic_read(&rdev->nr_pending);

		dist = abs(this_sector - conf->mirrors[disk].head_position);

		/* Don't change to another disk for sequential reads */

		if (conf->mirrors[disk].next_seq_sect == this_sector

		    || dist == 0) {

			int opt_iosize = bdev_io_opt(rdev->bdev) >> 9;

			struct raid1_info *mirror = &conf->mirrors[disk];



			/*

			 * If buffered sequential IO size exceeds optimal

			 * iosize, check if there is idle disk. If yes, choose

			 * the idle disk. read_balance could already choose an

			 * idle disk before noticing it's a sequential IO in

			 * this disk. This doesn't matter because this disk

			 * will idle, next time it will be utilized after the

			 * first disk has IO size exceeds optimal iosize. In

			 * this way, iosize of the first disk will be optimal

			 * iosize at least. iosize of the second disk might be

			 * small, but not a big deal since when the second disk

			 * starts IO, the first disk is likely still busy.

			 */

			if (test_bit(Nonrot, &rdev->flags) && opt_iosize > 0 &&

			    mirror->seq_start != MaxSector &&

			    mirror->next_seq_sect > opt_iosize &&

			    mirror->next_seq_sect - opt_iosize >=

			    mirror->seq_start) {

		if (is_sequential(conf, disk, r1_bio)) {

			if (!should_choose_next(conf, disk)) {

				best_disk = disk;

				break;

			}

			/*

			 * Add 'pending' to avoid choosing this disk if

			 * there is other idle disk.
@@ -801,10 +808,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect 
			 * will be chosen.

			 */

			sequential_disk = disk;

			} else {

				best_disk = disk;

				break;

			}

		}



		if (min_pending > pending) {