for the long answer, grep MAXDSIZ in the kernel. basically, it sets
the size of the heap, which can't be used for other things like mmap().
when this came up two weeks ago, the guy tried it and later told me
"yeah, it didn't work too well". your experience may be different, but
you're on your own.
http://marc.theaimsgroup.com/?t=111731093400001&r=1&w=2