Quite the same problem is found as in http://www.cpanforum.com/threads/3033

Jon Nistor (nistor@snickers.org) has reported that Perl 5.8.5 on Linux with the latest upgraded threads and threads::shared still experiences consant memory footprint growth. When threading support in Torrus is switched off, memory leaks are not present.

Here's the code that deals with the threading: Torrus::Collector::RRDStorage. There's a semaphore that is put down every time the process accesses the RRDtool procedures, and "sub rrdUpdateThread" on Line 504 performs the RRD store operations in the background.

Jon has also tried to downgrade the modules to 1.57 and 1.06, with the same results.