Perl won't release memory back to the operating system at runtime, only on global destruction as the script terminates. However, Perl will re-use the memory that it has allocated and that it is no longer using. For example, if you declare a lexical variable in one scope and load it up with 30MB of data, but then let that variable fall out of scope, Perl should be able to re-use that memory space.

Places to look:

• Circular references: These can cause memory leaks since the memory never has its reference count drop to zero, Perl can't re-claim it for internal use.
• Modules: Are you using half of CPAN? There's nothing wrong with using Moose, DBIx::Class, and many of the other slightly heavy distributions on CPAN, but they do use memory.
• Scoping: Are you allowing lexical variables to fall out of scope? (You should be.) Program with the objective of keeping state as ephemeral as possible; let variables have the narrowest possible scope - particularly those that are holding large chunks.
• File/Database handling: Are you slurping in large files or large Database query data sets? Process smaller chunks at a time.
• Stability: Once your process grows to 30MB, does it stay there, or does it grow further over time? Frankly, even if it's consuming 100MB, that's not the end of the world as long as you can count on it staying close to that plateau. If it keeps on growing over time, you've got a bigger problem (a memory leak). A well-behaved process that hits a memory plateau and stays there is usually acceptable.
• Tools: Try valgrind, Devel::LeakTrace, Devel::MemoryTrace::Lite, and other such tools can help you to watch how memory is growing and being used.