The flushing of the InnoDB temporary tablespace is unnecessarily tied to the write-ahead redo logging and the flushing of the persistent tablespaces.
It would be good to avoid any writes to the temporary tablespace, unless the pages are being evicted from the buffer pool and going to be reused.
This task is one step towards that goal: When a page in a temporary tablespace is marked as free, we should remove the page from the flush list. This will avoid unnecessary writes of garbage that is certainly not needed any more. (The freed pages would never be read back; instead new pages would be created.)