There are a couple of large red flags here, but why not just use an array instead of an arena allocator and a linked list (of pointers I'm guessing).
If you need a linked list, use an array with indices and you can cut the size in half if you don't need 64 bit integers. If it has to be enormous, make a linked list of arrays for better locality.
If you need a linked list, use an array with indices and you can cut the size in half if you don't need 64 bit integers. If it has to be enormous, make a linked list of arrays for better locality.