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Commit 80cfd548 authored by Jens Axboe's avatar Jens Axboe
Browse files

[BLOCK] bio: check for same page merge possibilities in __bio_add_page() 



For filesystems with a blocksize < page size, we can merge same page
calls into the bio_vec at the end of the bio. This saves segments
on systems with a page size > the "normal" 4kb fs block size.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarJens Axboe <axboe@suse.de>
parent 88ee5ef1

fs/bio.c

+24 −2
Original line number Diff line number Diff line
@@ -325,10 +325,31 @@ static int __bio_add_page(request_queue_t *q, struct bio *bio, struct page 
	if (unlikely(bio_flagged(bio, BIO_CLONED)))

		return 0;



	if (bio->bi_vcnt >= bio->bi_max_vecs)

	if (((bio->bi_size + len) >> 9) > max_sectors)

		return 0;



	if (((bio->bi_size + len) >> 9) > max_sectors)

	/*

	 * For filesystems with a blocksize smaller than the pagesize

	 * we will often be called with the same page as last time and

	 * a consecutive offset.  Optimize this special case.

	 */

	if (bio->bi_vcnt > 0) {

		struct bio_vec *prev = &bio->bi_io_vec[bio->bi_vcnt - 1];



		if (page == prev->bv_page &&

		    offset == prev->bv_offset + prev->bv_len) {

			prev->bv_len += len;

			if (q->merge_bvec_fn &&

			    q->merge_bvec_fn(q, bio, prev) < len) {

				prev->bv_len -= len;

				return 0;

			}



			goto done;

		}

	}



	if (bio->bi_vcnt >= bio->bi_max_vecs)

		return 0;



	/*
@@ -382,6 +403,7 @@ static int __bio_add_page(request_queue_t *q, struct bio *bio, struct page 
	bio->bi_vcnt++;

	bio->bi_phys_segments++;

	bio->bi_hw_segments++;

 done:

	bio->bi_size += len;

	return len;

}