The article says exactly this in bold at the bottom:

> If you can break up a task into many parts, each of which is highly local, then memory access in each part will be O(1). GPUs are already often very good at getting precisely these kinds of efficiencies. But if the task requires a lot of memory interdependencies, then you will get lots of O(N^⅓) terms. An open problem is coming up with mathematical models of computation that are simple but do a good job of capturing these nuances.