in reply to
How to return unused memory to OS?
Your analysis is basically correct. Once Perl has claimed the memory from the OS it will not be returned to the OS' pool.
A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James