Why do I have to spend a lot of time in checking permissions when I drop table?

Yesterday, I drop a table in checking permissions spent 20s+, this time spent where? Often looking to find my profile innodb_file_per_table=1, InnoDB needs to traverse the LRU list and discard the pages in the table space that belong to the table. If the InnoDB buffer pool is large, it takes a long time, and Table_cache locks cannot be held by other query statements when performing this action.

Resources:

https://www.percona.com/blog/2011/02/03/performance-problem-with-innodb-and-drop-table/

https://www.percona.com/blog/2011/04/20/drop-table-performance/

Why do I have to spend a lot of time in checking permissions when I drop table?