in reply to
Re^4: How to deal with the fact that Perl is not releasing memory
in thread How to deal with the fact that Perl is not releasing memory
Anything allocated will not be released to the operating system. See e.g. http://c-faq.com/malloc/free2os.es.html. The exception to this is mmapped memory, typically used for fast file access.
I suspect your primary problem is the actual parsing of the humongous HTML pages. It just takes a lot of memory -- but the memory should still be freed and reused by the Perl interpreter. But I found this choice quote from HTML::TreeBuilder:
4. previous versions of HTML::TreeBuilder required you to call $tree->delete() to erase the contents of the tree from memory when you're done with the tree. This is not normally required anymore. See "Weak References" in HTML::Element for details.
One general technique for keeping the memory use to a minimum is to fork off a child for every (large) request, and pass the bare-minimum result (here, @messages) to the parent. It's far from elegant and relatively difficult to implement, and the peak memory use will still be the same -- just not in the parent process. A last-resort option.