I must apologize for having blamed Maxima, as it really seems to be
an OS problem. I just took out my 3-year-old netbook (you can all
imagine how "powerful" this is) and it seamlessly runs one of my
tests that did not complete on a brand new 27" iMac with 4GB of RAM
due to insufficient memory.
Tests on two different Linux machine, one being a 7-year-old desktop
computer, show that Maxima gets memory assigned, more and more
during the test, but not beyond a certain limit (e.g. 15 or 20%).
I have now just completed a two hour test and almost immediately
after completion Maxima gave back all that used RAM to the system.
Best regards
Philipp
PS: This time, it's GCL with 5.25 and 5.20, one on Debian, one on Ubuntu