f2fs: avoid allocating failure in bio_alloc

This patch add macro MAX_BIO_BLOCKS to limit value of npages in
f2fs_bio_alloc, it can avoid allocating failure in bio_alloc caused by
npages is larger than BIO_MAX_PAGES.

Signed-off-by: Yu Chao <chao2.yu@samsung.com>
Reviewed-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 09af9c7..bd79bbe 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -657,6 +657,7 @@
 				block_t blk_addr, enum page_type type)
 {
 	struct block_device *bdev = sbi->sb->s_bdev;
+	int bio_blocks;
 
 	verify_block_addr(sbi, blk_addr);
 
@@ -676,7 +677,8 @@
 			goto retry;
 		}
 
-		sbi->bio[type] = f2fs_bio_alloc(bdev, max_hw_blocks(sbi));
+		bio_blocks = MAX_BIO_BLOCKS(max_hw_blocks(sbi));
+		sbi->bio[type] = f2fs_bio_alloc(bdev, bio_blocks);
 		sbi->bio[type]->bi_sector = SECTOR_FROM_BLOCK(sbi, blk_addr);
 		sbi->bio[type]->bi_private = priv;
 		/*