My point is not speed of forking, but memory pressure. We have problems with
Nix package manager forking any apps, unless it uses vfork() (either
directly, or indirectly via posix_spawn).

If zombies are the only reason for double forking, there are other ways
around, e. g. ignoring SIGCHLD.

And speaking of bugs, don't we have tests? :-)

Old plain fork is expensive, even on Linux, maybe because of garbage
collector.

https://github.com/zalora/defnix/commit/987a49aa77be5596ec2a352c1c758bce532b
5818
https://github.com/zalora/nix-
exec/commit/ea6eb396f0fa67df6568e1bf5dada41fb70a6ca2