- Currently page cleaner thread will stop flushing if
  dirty_pct < innodb_max_dirty_pages_pct_lwm.

- If the server is not performing any activity then said resources/time
  could be used to flush the pending dirty pages and keep buffer pool
  clean for the next burst of the cycle. This flushing is called idle flushing.

- flushing logic underwent a complete revamp in 10.5.7/8
  and as part of the revamp idle flushing logic got removed.

- New proposed logic of idle flushing is based on updated logic of the
  page cleaner that will enable idle flushing if
  - buf page cleaner is idle
  - there are dirty pages (< innodb_max_dirty_pages_pct_lwm)
  - server is not performing any activity

  Logic will kickstart the idle flushing bounded by innodb_io_capacity.

(Thanks to Marko Makela for reviewing the patch and idea
 right from the its inception).