Summit node CPUs can access GPU memory coherently and unified memory allows for a single pointer across all processors. On most systems that involves page faults migrating pages, but summit has something called ATS that allows GPU to directly access all system memory.

https://vimeo.com/262870773/recommended

Think of it as a much higher bandwidth PCIE. You still have to think about data locality, the same way you do with cpu cache levels. It just makes the problem of not having data on the gpu less painful than before.