http://code.google.com/p/rubyenterpriseedition/issues/detail?id=67
Use mmap() to allocate heaps by default. Use mmap() MAP_ANON, instead of /dev/zero. Align mmap() size to pagesize. Align heap allocation size to pagesize. Expand heap slotlimit to fit in aligned allocation. New $RUBY_HEAP_* options: RUBY_HEAP_INIT_SLOTS=N initial number of slots per heap. RUBY_HEAP_MIN_SLOTS=N value is independent of RUBY_HEAP_INIT_SLOTS. RUBY_HEAP_MAX_SLOTS=N max number slots for a heap. RUBY_HEAP_PAGESIZE=bytes defaults to PAGESIZE or 4096. RUBY_HEAP_SLOTS_INCREMENT=N allow 0. Refactor set_gc_parameters().