That makes sense. For example, your redis instance will have fixed RAM, so might as well pre-allocate it at boot and avoid fragmentation. Memcached works simil

That makes sense. For example, your redis instance will have fixed RAM, so might as well pre-allocate it at boot and avoid fragmentation. Memcached works similarly (slabs of fixed size), except they are not pre-allocated. If you're sharing hardware with multiple services, e.g. web, database, cache, the kind of performance this is targeting isn't a priority.