It's a configurable limit. 64MB is just what he set the limit to for that particular group, that's what the "64<<20" in the NewGroup call is for. You could configure it to use many gigabytes.
The fact it doesn't have cache expiration times or inc/dec discards it as memcache replacement, at least for me. Well, and the fact that only go is supported at the moment.
> 64 MB max per-node memory usage
So this is best used as a LRU cache of hot items.
It doesn't compete/replace memcache comprehensively, but it does attack the use of memcache as a relief for hot items.
I can see me mixing my Go programs with both groupcache and memcache.
Edit: I have glanced through the code and cannot see where the 64 MB per-node limit comes in. Anyone see that?