block: blk-merge: fast-clone bio when splitting rw bios (52cc6eea) · Commits · 戴 / test

biovecs has become immutable since v3.13, so it isn't necessary to allocate biovecs for the new cloned bios, then we can save one extra biovecs allocation/copy, and the allocation is often not fixed-length and a bit more expensive. For example, if the 'max_sectors_kb' of null blk's queue is set as 16(32 sectors) via sysfs just for making more splits, this patch can increase throught about ~70% in the sequential read test over null_blk(direct io, bs: 1M). Cc: Christoph Hellwig <hch@infradead.org> Cc: Kent Overstreet <kent.overstreet@gmail.com> Cc: Ming Lin <ming.l@ssi.samsung.com> Cc: Dongsu Park <dpark@posteo.net> Signed-off-by:

Ming Lei <ming.lei@canonical.com> This fixes a performance regression introduced by commit , and allows us to take full advantage of the fact that we have immutable bio_vecs. Hand applied, as it rejected violently with commit . Signed-off-by:

Jens Axboe <axboe@fb.com>

block/blk-merge.c

+4 −15

Original line number	Diff line number	Diff line
		@@ -66,15 +66,12 @@ static struct bio blk_bio_segment_split(struct request_queue q,
		struct bio *bio,
		struct bio_set *bs)
		{
		struct bio *split;
		struct bio_vec bv, bvprv, *bvprvp = NULL;
		struct bvec_iter iter;
		unsigned seg_size = 0, nsegs = 0, sectors = 0;

		bio_for_each_segment(bv, bio, iter) {
		sectors += bv.bv_len >> 9;

		if (sectors > queue_max_sectors(q))
		if (sectors + (bv.bv_len >> 9) > queue_max_sectors(q))
		goto split;

		/*
		@@ -95,6 +92,7 @@ static struct bio blk_bio_segment_split(struct request_queue q,
		seg_size += bv.bv_len;
		bvprv = bv;
		bvprvp = &bv;
		sectors += bv.bv_len >> 9;
		continue;
		}
		new_segment:
		@@ -105,21 +103,12 @@ new_segment:
		bvprv = bv;
		bvprvp = &bv;
		seg_size = bv.bv_len;
		sectors += bv.bv_len >> 9;
		}

		return NULL;
		split:
		split = bio_clone_bioset(bio, GFP_NOIO, bs);

		split->bi_iter.bi_size -= iter.bi_size;
		bio->bi_iter = iter;

		if (bio_integrity(bio)) {
		bio_integrity_advance(bio, split->bi_iter.bi_size);
		bio_integrity_trim(split, 0, bio_sectors(split));
		}

		return split;
		return bio_split(bio, sectors, GFP_NOIO, bs);
		}

		void blk_queue_split(struct request_queue q, struct bio *bio,

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