From 80cfd548eed68cf90c5ae9cfcd6b02230cece756 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Fri, 6 Jan 2006 09:43:28 +0100 Subject: [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: Christoph Hellwig Signed-off-by: Jens Axboe --- fs/bio.c | 26 ++++++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-) diff --git a/fs/bio.c b/fs/bio.c index 38d3e8023a07..dfe242a21eb4 100644 --- a/fs/bio.c +++ b/fs/bio.c @@ -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; } -- cgit v1.2.3