1. Docu here: https://mariadb.com/kb/en/aria-status-variables/
could be more clear that:

• Aria_pagecache_blocks_unused is the current state
• Aria_pagecache_blocks_used is a high water mark from somewhen in the past

2. Docu here: https://mariadb.com/kb/en/aria-status-variables/
and here: https://mariadb.com/kb/en/flush/#flush-status

states that this 3 status variables:

Aria_pagecache_blocks_not_flushed
Aria_pagecache_blocks_unused
Aria_pagecache_blocks_used

can be reset with flush status. This does IMHO technically not make sense (at least for not_flushed and unused, possibly it does make sense for the high water mark used) but experiments show that flush status does not reset the values:

root@mariadb-105 [test] SQL> show global status like 'aria%';
-----------------------------------------+

-----------------------------------------+

-----------------------------------------+
8 rows in set (0.001 sec)

root@mariadb-105 [test] SQL> flush status;
Query OK, 0 rows affected (0.000 sec)

root@mariadb-105 [test] SQL> show global status like 'aria%';
-----------------------------------------+

-----------------------------------------+

-----------------------------------------+
8 rows in set (0.001 sec)

root@mariadb-105 [test] SQL> flush tables;
Query OK, 0 rows affected (0.042 sec)

root@mariadb-105 [test] SQL> flush status;
Query OK, 0 rows affected (0.000 sec)

root@mariadb-105 [test] SQL> show global status like 'aria%';
-----------------------------------------+

-----------------------------------------+

-----------------------------------------+
8 rows in set (0.001 sec)

This should be fixed or at least clarified...