We don't really need to know how much. We need to know if it grows without stopping. A persistent application that does a lot *will* grow and might grow large. It will, however, stop growing at some point unless it has leaks.

I think you have mischaracterized OSes and Perl with regards to memory management. Lazy means nothing here, storage is a misnomer, garbage collection and allocation in Perl have nothing to do with competition.

Test::Memory::Cycle sounds like a promising idea. It would be nice to see how to apply it to an FCGI process. Without that extra step, the suggestion seems like CPAN-BINGO handwaving. It's not teaching to fish as much as saying: Fish live in water and there's a lake over yonder.

The psgix.harakiri suggestion is sound if there is a memory leak that can't be easily solved but without knowing if the OP is using PSGI it's as likely a pointless suggestion as a good one.