f2fs: fix wrong block count instead of bytes

We should convert cur_lblock, a block count, to bytes for len.

Fixes: af4b6b8e ("f2fs: introduce check_swap_activate_fast()")
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -3893,7 +3893,7 @@ static int check_swap_activate_fast(struct swap_info_struct *sis,
 	sector_t highest_pblock = 0;
 	int nr_extents = 0;
 	unsigned long nr_pblocks;
-	unsigned long len;
+	u64 len;
 	int ret;
 
 	/*
@@ -3911,7 +3911,7 @@ static int check_swap_activate_fast(struct swap_info_struct *sis,
 		cond_resched();
 
 		memset(&map_bh, 0, sizeof(struct buffer_head));
-		map_bh.b_size = len - cur_lblock;
+		map_bh.b_size = len - blks_to_bytes(inode, cur_lblock);
 
 		ret = get_data_block(inode, cur_lblock, &map_bh, 0,
 					F2FS_GET_BLOCK_FIEMAP, &next_pgofs);