[PATCH 42/60] block: use bio_for_each_segment_mp() to compute segments count

@@ -86,6 +86,61 @@ static inline unsigned get_max_io_size(struct request_queue *q,
 	return sectors;
 }
 
+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 old_nsegs = *nsegs;
+	unsigned new_nsegs, seg_size;
+
+	WARN_ON(old_nsegs == queue_max_segments(q));
+	WARN_ON(bv->bv_len == 0);
+
+	/*
+	 * Multipage bvec is too big to hold in one segment,
+	 * so the current bvec has to be splitted as multiple
+	 * segments.
+	 *
+	 * @seg_size is segment size of last segment in this bvec
+	 * @new_nsegs is segment count of this bvec
+	 */
+	seg_size = bv->bv_len % queue_max_segment_size(q);
+	new_nsegs = bv->bv_len / queue_max_segment_size(q);
+	if (!seg_size)
+		seg_size = queue_max_segment_size(q);
+	else
+		new_nsegs += 1;
+
+	/* need splitting if max segs is reached */
+	if (old_nsegs + new_nsegs > queue_max_segments(q)) {
+		new_nsegs = queue_max_segments(q) - old_nsegs;
+
+		/* split the bvec */
+		if (bv->bv_len > queue_max_segment_size(q))
+			seg_size = queue_max_segment_size(q);
+		need_split = true;
+	}
+
+	/* update front segment size */
+	if (!old_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;
+	}
+
+	*last_seg_size = seg_size;
+	*nsegs += new_nsegs;
+
+	if (sectors)
+		*sectors += ((new_nsegs - 1) *
+				queue_max_segment_size(q) + seg_size) >> 9;
+
+	return need_split;
+}
+
 static struct bio *blk_bio_segment_split(struct request_queue *q,
 					 struct bio *bio,
 					 struct bio_set *bs,

@@ -101,7 +156,7 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 	unsigned bvecs = 0;
 	unsigned advance;
 
-	bio_for_each_segment(bv, bio, iter) {
+	bio_for_each_segment_mp(bv, bio, iter) {
 		/*
 		 * With arbitrary bio size, the incoming bio may be very
 		 * big. We have to split the bio into small bios so that

@@ -138,8 +193,12 @@ 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);
 			}
 			if (sectors)
 				goto split;

@@ -180,11 +239,12 @@ 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;
 
 		/* restore the bvec for iterator */
 		bv.bv_len += advance;

@@ -253,6 +313,7 @@ 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;
 

@@ -274,7 +335,7 @@ 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_segment_mp(bv, bio, iter) {
 			/*
 			 * If SG merging is disabled, each bio vector is
 			 * a segment

@@ -296,20 +357,20 @@ 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;