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From: Ming Lei <ming.lei@redhat.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	Ming Lei <ming.lei@redhat.com>, Christoph Hellwig <hch@lst.de>
Subject: [PATCH V9 03/19] block: use bio_for_each_bvec() to compute multi-page bvec count
Date: Tue, 13 Nov 2018 23:14:49 +0800	[thread overview]
Message-ID: <20181113151505.15498-4-ming.lei@redhat.com> (raw)
In-Reply-To: <20181113151505.15498-1-ming.lei@redhat.com>

First it is more efficient to use bio_for_each_bvec() in both
blk_bio_segment_split() and __blk_recalc_rq_segments() to compute how
many multi-page bvecs there are in the bio.

Secondly once bio_for_each_bvec() is used, the bvec may need to be
splitted because its length can be very longer than max segment size,
so we have to split the big bvec into several segments.

Thirdly when splitting multi-page bvec into segments, the max segment
limit may be reached, so the bio split need to be considered under
this situation too.

Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-merge.c | 90 ++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 76 insertions(+), 14 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 91b2af332a84..6f7deb94a23f 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -160,6 +160,62 @@ static inline unsigned get_max_io_size(struct request_queue *q,
 	return sectors;
 }
 
+/*
+ * Split the bvec @bv into segments, and update all kinds of
+ * variables.
+ */
+static bool bvec_split_segs(struct request_queue *q, struct bio_vec *bv,
+		unsigned *nsegs, unsigned *last_seg_size,
+		unsigned *front_seg_size, unsigned *sectors)
+{
+	bool need_split = false;
+	unsigned len = bv->bv_len;
+	unsigned total_len = 0;
+	unsigned new_nsegs = 0, seg_size = 0;
+
+	if ((*nsegs >= queue_max_segments(q)) || !len)
+		return need_split;
+
+	/*
+	 * Multipage bvec may be too big to hold in one segment,
+	 * so the current bvec has to be splitted as multiple
+	 * segments.
+	 */
+	while (new_nsegs + *nsegs < queue_max_segments(q)) {
+		seg_size = min(queue_max_segment_size(q), len);
+
+		new_nsegs++;
+		total_len += seg_size;
+		len -= seg_size;
+
+		if ((queue_virt_boundary(q) && ((bv->bv_offset +
+		    total_len) & queue_virt_boundary(q))) || !len)
+			break;
+	}
+
+	/* split in the middle of the bvec */
+	if (len)
+		need_split = true;
+
+	/* update front segment size */
+	if (!*nsegs) {
+		unsigned first_seg_size = seg_size;
+
+		if (new_nsegs > 1)
+			first_seg_size = queue_max_segment_size(q);
+		if (*front_seg_size < first_seg_size)
+			*front_seg_size = first_seg_size;
+	}
+
+	/* update other varibles */
+	*last_seg_size = seg_size;
+	*nsegs += new_nsegs;
+	if (sectors)
+		*sectors += total_len >> 9;
+
+	return need_split;
+}
+
 static struct bio *blk_bio_segment_split(struct request_queue *q,
 					 struct bio *bio,
 					 struct bio_set *bs,
@@ -173,7 +229,7 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 	struct bio *new = NULL;
 	const unsigned max_sectors = get_max_io_size(q, bio);
 
-	bio_for_each_segment(bv, bio, iter) {
+	bio_for_each_bvec(bv, bio, iter) {
 		/*
 		 * If the queue doesn't support SG gaps and adding this
 		 * offset would create a gap, disallow it.
@@ -188,8 +244,12 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 			 */
 			if (nsegs < queue_max_segments(q) &&
 			    sectors < max_sectors) {
-				nsegs++;
-				sectors = max_sectors;
+				/* split in the middle of bvec */
+				bv.bv_len = (max_sectors - sectors) << 9;
+				bvec_split_segs(q, &bv, &nsegs,
+						&seg_size,
+						&front_seg_size,
+						&sectors);
 			}
 			goto split;
 		}
@@ -214,11 +274,12 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 		if (nsegs == 1 && seg_size > front_seg_size)
 			front_seg_size = seg_size;
 
-		nsegs++;
 		bvprv = bv;
 		bvprvp = &bvprv;
-		seg_size = bv.bv_len;
-		sectors += bv.bv_len >> 9;
+
+		if (bvec_split_segs(q, &bv, &nsegs, &seg_size,
+					&front_seg_size, &sectors))
+			goto split;
 
 	}
 
@@ -296,6 +357,7 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 	struct bio_vec bv, bvprv = { NULL };
 	int cluster, prev = 0;
 	unsigned int seg_size, nr_phys_segs;
+	unsigned front_seg_size = bio->bi_seg_front_size;
 	struct bio *fbio, *bbio;
 	struct bvec_iter iter;
 
@@ -316,7 +378,7 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 	seg_size = 0;
 	nr_phys_segs = 0;
 	for_each_bio(bio) {
-		bio_for_each_segment(bv, bio, iter) {
+		bio_for_each_bvec(bv, bio, iter) {
 			/*
 			 * If SG merging is disabled, each bio vector is
 			 * a segment
@@ -336,20 +398,20 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 				continue;
 			}
 new_segment:
-			if (nr_phys_segs == 1 && seg_size >
-			    fbio->bi_seg_front_size)
-				fbio->bi_seg_front_size = seg_size;
+			if (nr_phys_segs == 1 && seg_size > front_seg_size)
+				front_seg_size = seg_size;
 
-			nr_phys_segs++;
 			bvprv = bv;
 			prev = 1;
-			seg_size = bv.bv_len;
+			bvec_split_segs(q, &bv, &nr_phys_segs, &seg_size,
+					&front_seg_size, NULL);
 		}
 		bbio = bio;
 	}
 
-	if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
-		fbio->bi_seg_front_size = seg_size;
+	if (nr_phys_segs == 1 && seg_size > front_seg_size)
+		front_seg_size = seg_size;
+	fbio->bi_seg_front_size = front_seg_size;
 	if (seg_size > bbio->bi_seg_back_size)
 		bbio->bi_seg_back_size = seg_size;
 
-- 
2.9.5


  parent reply	other threads:[~2018-11-13 15:15 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-13 15:14 [PATCH V9 00/19] block: support multi-page bvec Ming Lei
2018-11-13 15:14 ` [PATCH V9 01/19] block: introduce multi-page page bvec helpers Ming Lei
2018-11-13 15:14 ` [PATCH V9 02/19] block: introduce bio_for_each_bvec() Ming Lei
2018-11-13 15:14 ` Ming Lei [this message]
2018-11-13 15:14 ` [PATCH V9 04/19] block: use bio_for_each_bvec() to map sg Ming Lei
2018-11-13 15:14 ` [PATCH V9 05/19] block: introduce bvec_last_segment() Ming Lei
2018-11-13 15:14 ` [PATCH V9 06/19] fs/buffer.c: use bvec iterator to truncate the bio Ming Lei
2018-11-13 15:14 ` [PATCH V9 07/19] btrfs: use bvec_last_segment to get bio's last page Ming Lei
2018-11-13 15:14 ` [PATCH V9 08/19] btrfs: move bio_pages_all() to btrfs Ming Lei
2018-11-13 15:14 ` [PATCH V9 09/19] block: introduce bio_bvecs() Ming Lei
2018-11-13 15:14 ` [PATCH V9 10/19] block: loop: pass multi-page bvec to iov_iter Ming Lei
2018-11-13 15:14 ` [PATCH V9 11/19] bcache: avoid to use bio_for_each_segment_all() in bch_bio_alloc_pages() Ming Lei
2018-11-13 15:14 ` [PATCH V9 12/19] block: allow bio_for_each_segment_all() to iterate over multi-page bvec Ming Lei
2018-11-13 15:14 ` [PATCH V9 13/19] iomap & xfs: only account for new added page Ming Lei
2018-11-13 15:15 ` [PATCH V9 14/19] block: enable multipage bvecs Ming Lei
2018-11-13 15:15 ` [PATCH V9 15/19] block: always define BIO_MAX_PAGES as 256 Ming Lei
2018-11-13 15:15 ` [PATCH V9 16/19] block: document usage of bio iterator helpers Ming Lei
2018-11-13 15:15 ` [PATCH V9 17/19] block: don't use bio->bi_vcnt to figure out segment number Ming Lei
2018-11-13 15:15 ` [PATCH V9 18/19] block: kill QUEUE_FLAG_NO_SG_MERGE Ming Lei
2018-11-13 15:15 ` [PATCH V9 19/19] block: kill BLK_MQ_F_SG_MERGE Ming Lei
2018-11-14  2:44 ` [PATCH V9 00/19] block: support multi-page bvec Dave Chinner
2018-11-14  2:57   ` Ming Lei
2018-11-14 15:22   ` Christoph Hellwig
2018-11-15  9:35     ` Ming Lei

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