Messages in this thread | | | Date | Mon, 30 Jun 2008 13:37:39 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] fix bio_add_page for non trivial merge_bvec_fn case |
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On Sun, 08 Jun 2008 19:45:08 +0400 Dmitri Monakhov <dmonakhov@openvz.org> wrote:
> We have to properly decrease all related bio's counters, especially bi_size > in order to merge_bvec_fn return right result. Usually 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. >
Please cc Jens on BIO changes.
> --- > fs/bio.c | 16 ++++++++++++---- > 1 files changed, 12 insertions(+), 4 deletions(-) > > diff --git a/fs/bio.c b/fs/bio.c > index 7856257..d713074 100644 > --- a/fs/bio.c > +++ b/fs/bio.c > @@ -332,14 +332,21 @@ 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) { > + /* Temprory detacth last bio_vec. */
whoa, drunken speling.
> + bio->bi_size -= prev->bv_len; > + bio->bi_vcnt--; > + bio->bi_phys_segments--; > + bio->bi_hw_segments--; > + > prev->bv_len += len; > if (q->merge_bvec_fn && > q->merge_bvec_fn(q, bio, prev) < len) { > prev->bv_len -= len; > - return 0; > + len = 0; > } > > - goto done; > + bio->bi_size += prev->bv_len; > + goto out_add_bvec; > } > } > > @@ -394,11 +401,12 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page > BIOVEC_VIRT_MERGEABLE(bvec-1, bvec))) > bio->bi_flags &= ~(1 << BIO_SEG_VALID); > > + bio->bi_size += len; > +out_add_bvec: > bio->bi_vcnt++; > bio->bi_phys_segments++; > bio->bi_hw_segments++; > - done: > - bio->bi_size += len; > return len; > }
For some reason patch(1) claims this hunk was corrupted. I typed it in by hand.
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