Apparently there is a bug
This is apparently a bug
From Kurtvm's Blog
Bug 10211065.-P Base Bug 9796810
Abstract: MEMORY FOOTPRINT FOR DEDICATED SERVER PROCESSES MORE THAN DOUBLED AFTER 11G UGP
Bug 9796810.-P Base Bug 10190759
Abstract: 11G SERVER PROCESSES CONSUMING MUCH MORE MEMORY THAT 10G OR 9I
Bug 10190759.-P
Abstract: PROCESSES CONSUMING ADDITIONAL MEMORY DUE TO 'USLA HEAP'
The good news is - there's a 'interim' patch - number 10190759.
On to patching my environments.