How it feels when you realize that, something going to be scary in term of question – “Wait, why? how?”
Let’s see:

I am trying to allocate 9G buffer pool size with 64 instances:

innodb_buffer_pool_instances=64
innodb_buffer_pool_size=9G

From error log it said that:

InnoDB: Initializing buffer pool, total size = 16G, instances = 64, chunk size = 128M

“Wait, why? how?” N1

From select it is also allocated 16G:

mysql> select @@innodb_buffer_pool_size/1024/1024/1024;
+------------------------------------------+
| @@innodb_buffer_pool_size/1024/1024/1024 |
+------------------------------------------+
| 16.000000000000 |
+------------------------------------------+

Just continue to increase pool size:

If you give 17G:

[Note] InnoDB: Initializing buffer pool, …