One of the best ways to minimize power consumed for RAM is to not have so %$*(%&(& much of it to begin with! Every machine is overprovisioned with RAM because the cost of swapping is so horrible. Is it possible to solve that problem instead? Can half of RAM be not just unpowered but actually removed from systems permanently (or never purchased to begin with)? That's the goal of RAMster (shameless plug, sorry)... which is built on top of cleancache and frontswap and zcache. Basically, it load-balances memory utilization across systems to achieve a maximum memory usage which is "max of sum" instead of "sum of max". Clearly that only works if you have a number of systems that statistically vary in working set size (i.e. doesn't help Amazon during the holiday shopping season), but that's still a big step forward.