… by lazily allocating PoolSubpages inside of the PoolArenas.
By default, a pooled allocator creates 32 arenas, and each arena, by default, makes room for 39 PoolSubpage size classes, which all told is 1.248 objects that serve no purpose other than as headers and locks for linked lists.
Each of these objects is at least 81 bytes, plus whatever the JVM adds on top.
This might not sound like much, but in our testing we'll be creating many thousands of allocators, and then it really adds up.
