Sorry about the previous report. I should have tested it thoroughly. Yes, it does not seem to rise but eventually it does. This time, I'v added garbage collection right after the subinterpreter is shutdown. The memory consumption does not seem to rise above 8MB when you start the test. But if you leave it running for couple of hours I have seen it grown upto 24MB. I haven't tested more that that but it seems that if you run it for couple of days, memory consumption will grow upto few 100 MB.
This is strange because mod_python doesn't seem to be doing anything special to handle this, then how does it work with mod_python?