block: check if page is mergeable in one helper

Now the check for deciding if one page is mergeable to current bvec
becomes a bit complicated, and we need to reuse the code before
adding pc page.

So move the check in one dedicated helper.

No function change.

Cc: Omar Sandoval <osandov@fb.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -647,6 +647,24 @@ struct bio *bio_clone_fast(struct bio *bio, gfp_t gfp_mask, struct bio_set *bs)
 }
 EXPORT_SYMBOL(bio_clone_fast);
 
+static inline bool page_is_mergeable(const struct bio_vec *bv,
+		struct page *page, unsigned int len, unsigned int off,
+		bool same_page)
+{
+	phys_addr_t vec_end_addr = page_to_phys(bv->bv_page) +
+		bv->bv_offset + bv->bv_len - 1;
+	phys_addr_t page_addr = page_to_phys(page);
+
+	if (vec_end_addr + 1 != page_addr + off)
+		return false;
+	if (xen_domain() && !xen_biovec_phys_mergeable(bv, page))
+		return false;
+	if (same_page && (vec_end_addr & PAGE_MASK) != page_addr)
+		return false;
+
+	return true;
+}
+
 /**
  *	bio_add_pc_page	-	attempt to add page to passthrough bio
  *	@q: the target queue
@@ -770,20 +788,12 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
 
 	if (bio->bi_vcnt > 0) {
 		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
-		phys_addr_t vec_end_addr = page_to_phys(bv->bv_page) +
-			bv->bv_offset + bv->bv_len - 1;
-		phys_addr_t page_addr = page_to_phys(page);
-
-		if (vec_end_addr + 1 != page_addr + off)
-			return false;
-		if (xen_domain() && !xen_biovec_phys_mergeable(bv, page))
-			return false;
-		if (same_page && (vec_end_addr & PAGE_MASK) != page_addr)
-			return false;
-
-		bv->bv_len += len;
-		bio->bi_iter.bi_size += len;
-		return true;
+
+		if (page_is_mergeable(bv, page, len, off, same_page)) {
+			bv->bv_len += len;
+			bio->bi_iter.bi_size += len;
+			return true;
+		}
 	}
 	return false;
 }