Your code still has alot of problems, like the unresponsiveness when trying to kill it. And the God-awful 98% cpu use for the xserver while running your script( probably caused by the constant redraws).The DrawingArea may not be the best choice of widget for doing this type of thing, although some really clever person may perfect it.

The Gnome2::Canvas is probably the best widget choice for this, see Gtk2 Scrolling Text.

Also check out GMeM -- a Gtk2 memory monitor utility for your future Gtk2 memory monitoring.