Once upon a time, there were few ways for one process to operate upon
another after its creation; sending signals and ptrace() were
about it. In recent years, interest in
providing ways for processes to control others has been on the increase,
and the kernel’s process-management API has been expanded accordingly.
Along these lines, the process_madvise() system call has been proposed as a way for one process to influence
how memory management is done in another. There is a new
process_madvise() series which is interesting in its own right,
but this series has also raised a couple of questions about how process
management should be improved in general.

Source: LWN.net – [$] process_madvise(), pidfd capabilities, and the revenge of the PIDs