Watching Tim Bunce - Profiling Memory Usage (YAPC-NA 2013) is an excellent way to come to a better understanding of how Perl manages memory.

Most memory leaks can be traced back to XS code, or to circular references. There are other possible sources (some are mentioned in his talk), but those are the big ones. At any rate, I really enjoyed that talk, and although I thought I knew a lot about Perl's memory management, the talk showed me that I still had a lot to learn, while also managing to provide a good dose of enlightenment. :)