1) that's virtual size, and most likely (depending on OS/cfg) COW (assuming no call to execve).

2) that's a default - most systems allow tuning

You can have pretty decent performance with forking models if you 1) have an upper bound for # of concurrent processes 2) have an input queue 3) cache results and serve from cache even for very small time windows. Not execve'ing is also a major benefit, if your system can do that (e.g. no mixing of threads with forks). In forking models, execve+runtime init is the largest overhead.

It will not beat other models, but forking processes offer other benefits such as memory protection, rlimits, namespace separation, capsicum/seccomp-bpf based sandboxing, ...

YMMV