97 lines
3.3 KiB
Diff
97 lines
3.3 KiB
Diff
From 5a8d75a1b8c99bdc926ba69b7b7dbe4fae81a5af Mon Sep 17 00:00:00 2001
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From: Ming Lei <ming.lei@redhat.com>
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Date: Fri, 14 Apr 2017 13:58:29 -0600
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Subject: [PATCH] block: fix bio_will_gap() for first bvec with offset
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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Commit 729204ef49ec("block: relax check on sg gap") allows us to merge
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bios, if both are physically contiguous. This change can merge a huge
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number of small bios, through mkfs for example, mkfs.ntfs running time
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can be decreased to ~1/10.
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But if one rq starts with a non-aligned buffer (the 1st bvec's bv_offset
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is non-zero) and if we allow the merge, it is quite difficult to respect
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sg gap limit, especially the max segment size, or we risk having an
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unaligned virtual boundary. This patch tries to avoid the issue by
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disallowing a merge, if the req starts with an unaligned buffer.
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Also add comments to explain why the merged segment can't end in
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unaligned virt boundary.
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Fixes: 729204ef49ec ("block: relax check on sg gap")
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Tested-by: Johannes Thumshirn <jthumshirn@suse.de>
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Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
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Signed-off-by: Ming Lei <ming.lei@redhat.com>
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Rewrote parts of the commit message and comments.
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Signed-off-by: Jens Axboe <axboe@fb.com>
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Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
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---
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include/linux/blkdev.h | 32 ++++++++++++++++++++++++++++----
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1 file changed, 28 insertions(+), 4 deletions(-)
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diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
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index 7548f332121a..01a696b0a4d3 100644
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--- a/include/linux/blkdev.h
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+++ b/include/linux/blkdev.h
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@@ -1672,12 +1672,36 @@ static inline bool bios_segs_mergeable(struct request_queue *q,
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return true;
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}
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-static inline bool bio_will_gap(struct request_queue *q, struct bio *prev,
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- struct bio *next)
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+static inline bool bio_will_gap(struct request_queue *q,
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+ struct request *prev_rq,
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+ struct bio *prev,
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+ struct bio *next)
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{
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if (bio_has_data(prev) && queue_virt_boundary(q)) {
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struct bio_vec pb, nb;
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+ /*
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+ * don't merge if the 1st bio starts with non-zero
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+ * offset, otherwise it is quite difficult to respect
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+ * sg gap limit. We work hard to merge a huge number of small
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+ * single bios in case of mkfs.
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+ */
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+ if (prev_rq)
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+ bio_get_first_bvec(prev_rq->bio, &pb);
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+ else
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+ bio_get_first_bvec(prev, &pb);
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+ if (pb.bv_offset)
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+ return true;
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+
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+ /*
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+ * We don't need to worry about the situation that the
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+ * merged segment ends in unaligned virt boundary:
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+ *
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+ * - if 'pb' ends aligned, the merged segment ends aligned
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+ * - if 'pb' ends unaligned, the next bio must include
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+ * one single bvec of 'nb', otherwise the 'nb' can't
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+ * merge with 'pb'
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+ */
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bio_get_last_bvec(prev, &pb);
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bio_get_first_bvec(next, &nb);
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@@ -1690,12 +1714,12 @@ static inline bool bio_will_gap(struct request_queue *q, struct bio *prev,
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static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
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{
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- return bio_will_gap(req->q, req->biotail, bio);
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+ return bio_will_gap(req->q, req, req->biotail, bio);
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}
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static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
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{
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- return bio_will_gap(req->q, bio, req->bio);
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+ return bio_will_gap(req->q, NULL, bio, req->bio);
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}
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int kblockd_schedule_work(struct work_struct *work);
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--
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2.11.0
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