Messages in this thread Patch in this message | | | Date | Thu, 04 Feb 2010 09:12:26 -0800 | From | Greg KH <> | Subject | [55/74] block: fix bio_add_page for non trivial merge_bvec_fn case |
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2.6.32-stable review patch. If anyone has any objections, please let us know.
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From: Dmitry Monakhov <dmonakhov@openvz.org>
commit 1d6165851cd8e3f919d446cd6da35dee44e8837e upstream.
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 fs_block_size == 1k and block device is raid0 with small chunk_size = 8k. Then it is impossible to merge 7-th fs-block in to bio which already has 6 fs-blocks.
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- fs/bio.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
--- a/fs/bio.c +++ b/fs/bio.c @@ -542,13 +542,18 @@ static int __bio_add_page(struct request if (page == prev->bv_page && offset == prev->bv_offset + prev->bv_len) { + unsigned int prev_bv_len = prev->bv_len; prev->bv_len += len; if (q->merge_bvec_fn) { struct bvec_merge_data bvm = { + /* prev_bvec is already charged in + bi_size, discharge it in order to + simulate merging updated prev_bvec + as new bvec. */ .bi_bdev = bio->bi_bdev, .bi_sector = bio->bi_sector, - .bi_size = bio->bi_size, + .bi_size = bio->bi_size - prev_bv_len, .bi_rw = bio->bi_rw, };
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