Commit 7ef6b12a authored by Ming Lin's avatar Ming Lin Committed by Jens Axboe
Browse files

md/raid5: split bio for chunk_aligned_read 



If a read request fits entirely in a chunk, it will be passed directly to the
underlying device (providing it hasn't failed of course).  If it doesn't fit,
the slightly less efficient path that uses the stripe_cache is used.
Requests that get to the stripe cache are always completely split up as
necessary.

So with RAID5, ripping out the merge_bvec_fn doesn't cause it to stop work,
but could cause it to take the less efficient path more often.

All that is needed to manage this is for 'chunk_aligned_read' do some bio
splitting, much like the RAID0 code does.

Cc: Neil Brown <neilb@suse.de>
Cc: linux-raid@vger.kernel.org
Acked-by: default avatarNeilBrown <neilb@suse.de>
Signed-off-by: default avatarMing Lin <ming.l@ssi.samsung.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent b49a0871

drivers/md/raid5.c

+32 −5
Original line number Diff line number Diff line
@@ -4800,7 +4800,7 @@ static int bio_fits_rdev(struct bio *bi) 
	return 1;

}



static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio)

static int raid5_read_one_chunk(struct mddev *mddev, struct bio *raid_bio)

{

	struct r5conf *conf = mddev->private;

	int dd_idx;
@@ -4809,7 +4809,7 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio) 
	sector_t end_sector;



	if (!in_chunk_boundary(mddev, raid_bio)) {

		pr_debug("chunk_aligned_read : non aligned\n");

		pr_debug("%s: non aligned\n", __func__);

		return 0;

	}

	/*
@@ -4886,6 +4886,31 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio) 
	}

}



static struct bio *chunk_aligned_read(struct mddev *mddev, struct bio *raid_bio)

{

	struct bio *split;



	do {

		sector_t sector = raid_bio->bi_iter.bi_sector;

		unsigned chunk_sects = mddev->chunk_sectors;

		unsigned sectors = chunk_sects - (sector & (chunk_sects-1));



		if (sectors < bio_sectors(raid_bio)) {

			split = bio_split(raid_bio, sectors, GFP_NOIO, fs_bio_set);

			bio_chain(split, raid_bio);

		} else

			split = raid_bio;



		if (!raid5_read_one_chunk(mddev, split)) {

			if (split != raid_bio)

				generic_make_request(raid_bio);

			return split;

		}

	} while (split != raid_bio);



	return NULL;

}



/* __get_priority_stripe - get the next stripe to process

 *

 * Full stripe writes are allowed to pass preread active stripes up until
@@ -5163,9 +5188,11 @@ static void make_request(struct mddev *mddev, struct bio * bi) 
	 * data on failed drives.

	 */

	if (rw == READ && mddev->degraded == 0 &&

	     mddev->reshape_position == MaxSector &&

	     chunk_aligned_read(mddev,bi))

	    mddev->reshape_position == MaxSector) {

		bi = chunk_aligned_read(mddev, bi);

		if (!bi)

			return;

	}



	if (unlikely(bi->bi_rw & REQ_DISCARD)) {

		make_discard_request(mddev, bi);

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