Some irssi users have reported that their irssi memory usage reaches 1-2 GB after a few months of usage. This time, the cause was a memory leak in Perl: https://rt.perl.org/Public/Bug/Display.html?id=130254
This bug affects Perl 5.24 (which is “current” in e.g. Debian Stable (Stretch)), and if you use certain regexes you will probably see memory leakage.
If you are suspecting a memory leak in irssi, here’s one way to find out more about the nature of your memory leak: dump irssi’s core using gcore. (irssi will be stopped during the dumping process but will carry on where it left off as soon as the dump is completed. If it takes a long time to dump the core, you may time out from some or all servers.) To do this, find irssi’s PID (by e.g. doing ps aux | grep irssi) and then execute:
gcore PID
You’ll get a core file that is as large as irssi’s memory usage at the time of the dump. If you have a memory leak due to the above Perl bug, you will have a lot of strings that start with “Assuming NOT a POSIX class” in your core file, which you can check using the following command:
strings core | grep "Assuming NOT a POSIX class" | wc
If this command outputs large numbers, your memory leak is most likely due to the above-mentioned Perl 5.24 bug. If you don’t get any output, you might still have a memory leak that can be found using the strings command. Either go through the output of the strings command manually and see if you can find any repeated messages, or maybe make use of the following command:
strings core | sort | uniq -c | sort -n -r | less
Let me or the people on #irssi on Freenode know if you find any other leaks.