LuaJIT doesn't have increased memory usage. 32 or 64 bit, it always packs pointers into the low bits of NaN doubles. Addresses fit because current 64 bit chips actually use 48 bit addresses.
(LuaJIT also uses a limited memory arena for allocations but it's not inherent to the design; it could be changed but the current garbage collector can't handle that much data)
(LuaJIT also uses a limited memory arena for allocations but it's not inherent to the design; it could be changed but the current garbage collector can't handle that much data)