See the links in my original post; all share memory between unrelated process. IPC::MM
looks very useful, but only shares memory between related processes, at least according to the MM docs at OSSP
(I haven't used it myself).
If you're not interested in doing the low-level work yourself (which will probably give the best performance at the expense of a lot of work), Cache::FastMmap might be helpful. It acts as a fast cache that sits in front of something else, like a database or DB file. You would mostly use the cache, and could periodically flush it out to the database to limit how much data you lose if your machine crashes. The author of this module has some interesting performance information at Comparison of different PERL caching modules.