I think I complained earlier about '+RTS -MxxxM' not being respected, but was unable to reproduce the issue. I just saw this again, my process was, I thought, limited to 800M heap, but, just before I gave up and killed the process, 'top' told me: 18580 ketil 18 0 1762m 945m 256 D 3.0 93.5 33:52.81 rbr So it used more than double the amount of memory. However, running the same executable with the same -M option on a different computer, it stayed firmly at 32139 ketil 25 0 779M 779M 872 R 99.8 9.9 16:17 0 rbr Apparently, there is some subtle difference between the two systems that causes the RTS's heap limitation to fail. The uname -a on the two systems say: -M works: Linux ... 2.4.21-32.0.1.ELsmp #1 SMP Wed May 25 13:51:11 EDT 2005 x86_64 x86_64 x86_64 GNU/Linux -M fails: Linux ... 2.6.9-22.EL #1 Sat Oct 8 17:48:27 CDT 2005 i686 i686 i386 GNU/Linux Let me know if there's any other information I can supply. -k -- If I haven't seen further, it is by standing in the footprints of giants