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Commit 862e5a5e authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

block: use bio_for_each_bvec() to map sg 



It is more efficient to use bio_for_each_bvec() to map sg, meantime
we have to consider splitting multipage bvec as done in blk_bio_segment_split().

Reviewed-by: default avatarOmar Sandoval <osandov@fb.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent dcebd755

block/blk-merge.c

+50 −20
Original line number Diff line number Diff line
@@ -464,6 +464,54 @@ static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio, 
	return biovec_phys_mergeable(q, &end_bv, &nxt_bv);

}



static struct scatterlist *blk_next_sg(struct scatterlist **sg,

		struct scatterlist *sglist)

{

	if (!*sg)

		return sglist;



	/*

	 * If the driver previously mapped a shorter list, we could see a

	 * termination bit prematurely unless it fully inits the sg table

	 * on each mapping. We KNOW that there must be more entries here

	 * or the driver would be buggy, so force clear the termination bit

	 * to avoid doing a full sg_init_table() in drivers for each command.

	 */

	sg_unmark_end(*sg);

	return sg_next(*sg);

}



static unsigned blk_bvec_map_sg(struct request_queue *q,

		struct bio_vec *bvec, struct scatterlist *sglist,

		struct scatterlist **sg)

{

	unsigned nbytes = bvec->bv_len;

	unsigned nsegs = 0, total = 0, offset = 0;



	while (nbytes > 0) {

		unsigned seg_size;

		struct page *pg;

		unsigned idx;



		*sg = blk_next_sg(sg, sglist);



		seg_size = get_max_segment_size(q, bvec->bv_offset + total);

		seg_size = min(nbytes, seg_size);



		offset = (total + bvec->bv_offset) % PAGE_SIZE;

		idx = (total + bvec->bv_offset) / PAGE_SIZE;

		pg = nth_page(bvec->bv_page, idx);



		sg_set_page(*sg, pg, seg_size, offset);



		total += seg_size;

		nbytes -= seg_size;

		nsegs++;

	}



	return nsegs;

}



static inline void

__blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,

		     struct scatterlist *sglist, struct bio_vec *bvprv,
@@ -481,25 +529,7 @@ __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec, 
		(*sg)->length += nbytes;

	} else {

new_segment:

		if (!*sg)

			*sg = sglist;

		else {

			/*

			 * If the driver previously mapped a shorter

			 * list, we could see a termination bit

			 * prematurely unless it fully inits the sg

			 * table on each mapping. We KNOW that there

			 * must be more entries here or the driver

			 * would be buggy, so force clear the

			 * termination bit to avoid doing a full

			 * sg_init_table() in drivers for each command.

			 */

			sg_unmark_end(*sg);

			*sg = sg_next(*sg);

		}



		sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);

		(*nsegs)++;

		(*nsegs) += blk_bvec_map_sg(q, bvec, sglist, sg);

	}

	*bvprv = *bvec;

}
@@ -521,7 +551,7 @@ static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio, 
	int nsegs = 0;



	for_each_bio(bio)

		bio_for_each_segment(bvec, bio, iter)

		bio_for_each_bvec(bvec, bio, iter)

			__blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,

					     &nsegs);