Experimental PACK_TIGHT compile time option
When set, the goal is to pack vnodes as tightly as possible - that is, to penalize wasted slots in assignments. One downside is that this will tend to make really lopsided mappings: eg. if you have 50 slots per pnode, and 51 vodes, you will end up mapping 50 to one and 1 to the other. The other downside is that I have not yet thought about how to balance this with link weights.