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().