dm bufio: use multi-page bio vector

The kernel supports multi page bio vector entries, so we can use them
in dm-bufio as an optimization.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

drivers/md/dm-bufio.c

@@ -1312,19 +1312,14 @@ static void use_bio(struct dm_buffer *b, enum req_op op, sector_t sector,
 {
 	struct bio *bio;
 	char *ptr;
-	unsigned int vec_size, len;
+	unsigned int len;
 
-	vec_size = b->c->block_size >> PAGE_SHIFT;
-	if (unlikely(b->c->sectors_per_block_bits < PAGE_SHIFT - SECTOR_SHIFT))
-		vec_size += 2;
-
-	bio = bio_kmalloc(vec_size, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOWARN);
+	bio = bio_kmalloc(1, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOWARN);
 	if (!bio) {
-dmio:
 		use_dmio(b, op, sector, n_sectors, offset);
 		return;
 	}
-	bio_init(bio, b->c->bdev, bio->bi_inline_vecs, vec_size, op);
+	bio_init(bio, b->c->bdev, bio->bi_inline_vecs, 1, op);
 	bio->bi_iter.bi_sector = sector;
 	bio->bi_end_io = bio_complete;
 	bio->bi_private = b;
@@ -1332,18 +1327,7 @@ static void use_bio(struct dm_buffer *b, enum req_op op, sector_t sector,
 	ptr = (char *)b->data + offset;
 	len = n_sectors << SECTOR_SHIFT;
 
-	do {
-		unsigned int this_step = min((unsigned int)(PAGE_SIZE - offset_in_page(ptr)), len);
-
-		if (!bio_add_page(bio, virt_to_page(ptr), this_step,
-				  offset_in_page(ptr))) {
-			bio_put(bio);
-			goto dmio;
-		}
-
-		len -= this_step;
-		ptr += this_step;
-	} while (len > 0);
+	__bio_add_page(bio, virt_to_page(ptr), len, offset_in_page(ptr));
 
 	submit_bio(bio);
 }