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.
Signed-off-by: Dmitri Monakhov <dmonakhov@xxxxxxxxxx>
---
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. */
+ 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;
}
--
1.5.4.rc4
--
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