From 1d6165851cd8e3f919d446cd6da35dee44e8837e Mon Sep 17 00:00:00 2001 From: Dmitry Monakhov Date: Wed, 27 Jan 2010 22:44:36 +0300 Subject: 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. Cc: Signed-off-by: Dmitry Monakhov Signed-off-by: Jens Axboe --- fs/bio.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'fs/bio.c') diff --git a/fs/bio.c b/fs/bio.c index 12429c9553eb..88094afc29ea 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, }; -- cgit v1.2.3