Replicating popular content is good if there's a smallish core set of popular content. Then you'd be able to serve popular content on the NIC it comes in on without cross NUMA traffic. Really depends on traffic distribution though, if you need to replicate a lot of content, then maybe you push too much content out of cache.

It'd be neat if you could teach the page cache to do replication for you... Then you might use SF_NOCACHE for not very popular content, no option medium content, and SF_NUMACACHE (or whatever) for content you wanted cached on the local NUMA node. I'm sure there's lots of dragons in there though ;)