On Sun, 08 Jun 2008 19:45:08 +0400
Dmitri Monakhov <dmonakhov@xxxxxxxxxx> 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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