This excessive memory consumption was seen on 3 machines, all of which run Debian. All three machines run p2pool as well as bitcoind. Two run XT, one runs Core.

I can't afford to do that. All of the servers I have are being used for something. Also, I'm not sure what it is you're trying to test for with that suggestion. The numbers I'm reporting are for bitcoind's resident set, not for the whole server's memory usage. I don't see how other processes running on the same machine are relevant unless you are suggesting that RPC calls (e.g. getblocktemplate) might be somehow responsible.

Not relevant. I addressed this message to both the Core and XT lists because the issue appears to affect both forks. Let's keep blocksize and governance debates to their own threads, please.

Repeating request: Has anyone else seen something similar? Can you report your mempool size and total bitcoind resident set size for your running full nodes?