Found it already. chinese instead of marys room yielded http://slatestarcodex.com/2014/09/01/book-review-and-highlights-quantum-computing-since-democritus/

If each page of the rule book corresponded to one neuron of a native speaker’s brain, then probably we’d be talking about a “rule book” at leas the size of the Earth, its pages searchable by a swarm of robots traveling at close to the speed of light. When you put it that way, maybe it’s not so hard to imagine this enormous Chinese-speaking entity that we’ve brought into being might have something we’d be prepared to call understanding or insight.