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Date: Tue, 26 Jan 2010 14:29:28 +0100 From: Jens Axboe <jens.axboe@...cle.com> To: Dmitry Monakhov <dmonakhov@...nvz.org> Cc: linux-kernel@...r.kernel.org Subject: Re: [PATCH] block: fix bio_add_page for non trivial merge_bvec_fn case 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 <dmonakhov@...nvz.org> > 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 <dmonakhov@...nvz.org> > --- > 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? -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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