fork() on Linux (and many other OSes) shares pages between the parent/child processes in a copy-on-write scheme
That doesn’t mean multiple long running processes will share memory though unless they actually create a shared mapping, which I think the gp is referring to.
In addition to tremendous memory waste this also kills cache performance.
I'd presume the persistence / I/O process would
be pretty short lived: its job is to save a snapshot to disk so there's not much reason to let it live long.
How does that share data between multiple Redis processes?