block: move the bi_vcnt check out of __bio_try_merge_page

Move the bi_vcnt out of __bio_try_merge_page and into the two callers
that don't already have it in preparation for additional changes to
__bio_try_merge_page.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jinyoung Choi <j-young.choi@samsung.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20230724165433.117645-5-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -945,10 +945,10 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
 static bool __bio_try_merge_page(struct bio *bio, struct page *page,
 		unsigned int len, unsigned int off, bool *same_page)
 {
-	if (bio->bi_vcnt > 0) {
 	struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
 
-		if (page_is_mergeable(bv, page, len, off, same_page)) {
+	if (!page_is_mergeable(bv, page, len, off, same_page))
+		return false;
 	if (bio->bi_iter.bi_size > UINT_MAX - len) {
 		*same_page = false;
 		return false;
@@ -956,9 +956,6 @@ static bool __bio_try_merge_page(struct bio *bio, struct page *page,
 	bv->bv_len += len;
 	bio->bi_iter.bi_size += len;
 	return true;
-		}
-	}
-	return false;
 }
 
 /*
@@ -1127,11 +1124,13 @@ int bio_add_page(struct bio *bio, struct page *page,
 	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
 		return 0;
 
-	if (!__bio_try_merge_page(bio, page, len, offset, &same_page)) {
+	if (bio->bi_vcnt > 0 &&
+	    __bio_try_merge_page(bio, page, len, offset, &same_page))
+		return len;
+
 	if (bio_full(bio, len))
 		return 0;
 	__bio_add_page(bio, page, len, offset);
-	}
 	return len;
 }
 EXPORT_SYMBOL(bio_add_page);
@@ -1205,14 +1204,14 @@ static int bio_iov_add_page(struct bio *bio, struct page *page,
 {
 	bool same_page = false;
 
-	if (!__bio_try_merge_page(bio, page, len, offset, &same_page)) {
-		__bio_add_page(bio, page, len, offset);
-		return 0;
-	}
-
+	if (bio->bi_vcnt > 0 &&
+	    __bio_try_merge_page(bio, page, len, offset, &same_page)) {
 		if (same_page)
 			bio_release_page(bio, page);
 		return 0;
+	}
+	__bio_add_page(bio, page, len, offset);
+	return 0;
 }
 
 static int bio_iov_add_zone_append_page(struct bio *bio, struct page *page,