The patch titled
block: fix bio_add_page for non trivial merge_bvec_fn case
has been added to the -mm tree. Its filename is
block-fix-bio_add_page-for-non-trivial-merge_bvec_fn-case.patch
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------------------------------------------------------
Subject: block: fix bio_add_page for non trivial merge_bvec_fn case
From: Dmitri Monakhov <dmonakhov@xxxxxxxxxx>
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>
Cc: Jens Axboe <jens.axboe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/bio.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff -puN fs/bio.c~block-fix-bio_add_page-for-non-trivial-merge_bvec_fn-case fs/bio.c
--- a/fs/bio.c~block-fix-bio_add_page-for-non-trivial-merge_bvec_fn-case
+++ a/fs/bio.c
@@ -332,14 +332,21 @@ static int __bio_add_page(struct request
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 +401,11 @@ static int __bio_add_page(struct request
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;
}
_
Patches currently in -mm which might be from dmonakhov@xxxxxxxxxx are
block-fix-bio_add_page-for-non-trivial-merge_bvec_fn-case.patch
block-fix-bio_add_page-for-non-trivial-merge_bvec_fn-case-fix.patch
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