stat = Off and ttl = 0, How does memory get freed when at capacity?

[Jakob Wildrain]

if I set ttl to 0 the cache entries will persist and if I set stat to Off then the entry will never be updated.

Now, Smarty caching engine creates compiled php templates that are also cached by xcache, and eventually the cache will run out of memory.

In this case, are older entries cleared out of cache or is the whole memory segment cleared out completely? Or how does this work?

Thank you.