f2fs: skip searching non-exist range in truncate_hole

Let's skip entire non-exist area to speed up truncate_hole by
using get_next_page_offset.
Signed-off-by: Weichao Guo <guoweichao@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -857,7 +857,7 @@ int truncate_hole(struct inode *inode, pgoff_t pg_start, pgoff_t pg_end)
 		err = get_dnode_of_data(&dn, pg_start, LOOKUP_NODE);
 		if (err) {
 			if (err == -ENOENT) {
-				pg_start++;
+				pg_start = get_next_page_offset(&dn, pg_start);
 				continue;
 			}
 			return err;