>From 65ac8c9a2988310a79215b68e9c93b6dca6c6665 Mon Sep 17 00:00:00 2001 From: Dmitry Monakhov Date: Wed, 27 Jan 2010 22:44:36 +0300 Subject: [PATCH] [PATCH] block: fix bio_add_page for non trivial merge_bvec_fn case We have to properly decrease bi_size in order to merge_bvec_fn return right result. Otherwise this result in false merge rejects for two absolutely valid bio_vecs. This may cause significant performance penalty for example fs_block_size == 1k and block device is raid0 with small chunk_size = 8k. Then it is impossible to merge 7-th fs-block in to bio which already has 6 fs-blocks. Signed-off-by: Dmitry Monakhov --- fs/bio.c | 7 ++++++- 1 files changed, 6 insertions(+), 1 deletions(-) diff --git a/fs/bio.c b/fs/bio.c index 76e6713..7448c7d 100644 --- a/fs/bio.c +++ b/fs/bio.c @@ -542,13 +542,18 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page if (page == prev->bv_page && offset == prev->bv_offset + prev->bv_len) { + unsigned int prev_bv_len = prev->bv_len; prev->bv_len += len; if (q->merge_bvec_fn) { struct bvec_merge_data bvm = { + /* prev_bvec is already charged in + bi_size, discharge it in order to + simulate merging updated prev_bvec + as new bvec. */ .bi_bdev = bio->bi_bdev, .bi_sector = bio->bi_sector, - .bi_size = bio->bi_size, + .bi_size = bio->bi_size - prev_bv_len, .bi_rw = bio->bi_rw, }; -- 1.6.3.3