[munificent]

I'm no expert either, but some of the literature I've read says that copying GCs aren't a panacea when it comes to improving locality. For some object graphs, they help, for others they actually reorder the objects in ways that make locality worse.

Consider, for example, a copying GC that copies using a depth-first traversal of the object graph and then running it over a tree that your program always processes in breadth-first order.