Contiguous memory allocation for drivers

Well, the defragmentation code obviously knows which regions can be defragmented: so there could be a memory zone that contains only allocations that defragmentation could move out of the way, plus regions that could be freed without writeout. I don't think this exists yet, though, and memory zones are single contiguous lumps, not a bunch of individually-contiguous regions like CMA produces. So I suppose 'is in a CMA region' would have to be another page flag or something. But we're perennially short of those...