关于innodb的问题，大家帮帮忙

innodb_buffer_pool_size 
InnoDB用来缓存它的数据和索引的内存缓冲区的大小。我理解是把索引和数据放在innodb_buffer_pool里操作会很快。服务器共16G内存， innodb_buffer_pool 设置的6G ，数据库里的innodb的数据+索引一共用了5G，innodb_buffer_pool 也占用了5G
于是我删除了一些比较大的innodb的表后
mysql> select sum(DATA_LENGTH),sum(INDEX_LENGTH) from information_schema.TABLES where engine="innodb" ;
+------------------+-------------------+
| sum(DATA_LENGTH) | sum(INDEX_LENGTH) |
+------------------+-------------------+
|       1669464064 |        1368981504 | 
+------------------+-------------------+innodb的数据+索引减少到了3G左右但是为什么Innodb_buffer_pool_pages_free还是那么少呢，已经删了这么多了
mysql> show status like '%innodb%'; 
+-----------------------------------+---------------+
| Variable_name                     | Value         |
+-----------------------------------+---------------+
| Com_show_innodb_status            | 0             | 
| Innodb_buffer_pool_pages_data     | 318940        | 
| Innodb_buffer_pool_pages_dirty    | 249           | 
| Innodb_buffer_pool_pages_flushed  | 162765981     | 
| Innodb_buffer_pool_pages_free     | 55101         | 
| Innodb_buffer_pool_pages_latched  | 0             | 
| Innodb_buffer_pool_pages_misc     | 19175         | 
| Innodb_buffer_pool_pages_total    | 393216        | 请教 我删除innodb大表以后，再执行什么操作才能使innodb_buffer_pool的占用减小，大家帮帮忙