How can you get a 32-bit machine to even recognize 8GB of RAM? I didn't think individual process size was the problem there. Are you talking about using PAE?
Comment on Re^6: persistent cache using Cache::FileCache
Linux supports up to 64GB RAM on 32-bit machines (CONFIG_NOHIGHMEM and nearby options). Not an expert here, but yes, the docs do say you need PAE. A single process won't be able to address all of it at once, but using memcached that doesn't change the usage semantics.