Dmitry Monakhov writes: > On Tue, Jan 26, 2010 at 4:29 PM, Jens Axboe wrote: >> On Tue, Jan 26 2010, Dmitry Monakhov wrote: >>> Hi, year ago I've sent a patch which fix false bio merge rejects, but >>> seems patch was missed. Currently the issue is still present. >>> >> >>> From 92a97ef181e15caa94bd56a1ade5c337db599b79 Mon Sep 17 00:00:00 2001 >>> From: Dmitry Monakhov >>> Date: Tue, 26 Jan 2010 16:01:34 +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 Itanium: page_size == 16k, fs_block_size == 1k and block device >>> is raid with small chunk_size. >>> >>> Signed-off-by: Dmitry Monakhov >>> --- >>>  fs/bio.c |    3 ++- >>>  1 files changed, 2 insertions(+), 1 deletions(-) >>> >>> diff --git a/fs/bio.c b/fs/bio.c >>> index 76e6713..9f8e517 100644 >>> --- a/fs/bio.c >>> +++ b/fs/bio.c >>> @@ -548,7 +548,8 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page >>>                               struct bvec_merge_data bvm = { >>>                                       .bi_bdev = bio->bi_bdev, >>>                                       .bi_sector = bio->bi_sector, >>> -                                     .bi_size = bio->bi_size, >>> +                                     .bi_size = bio->bi_size - >>> +                                                     (prev->bv_len - len), >>>                                       .bi_rw = bio->bi_rw, >>>                               }; >> >> Hmm confused. why isn't this just bio->bi_size - len? I've attached more descriptive version of the patch. Jens, please clarify your opinion to the patch( do you like it or not?) I don't want it miss again.