On Fri, 8 May 2020 11:36:53 -0700 Minchan Kim [off-list ref] wrote:

...

Per Vlastimil's request, I changed "which and advise" with "idtype and
advice" in function prototype of description.
Could you replace the part in the description? Code is never changed.

Done, but...

...

There is a demand[1] to support pid as well pidfd for process_madvise to
reduce unnecessary syscall to get pidfd if the user has control of the
target process(ie, they could guarantee the process is not gone or pid is
not reused).

This patch aims for supporting both options like waitid(2).  So, the
syscall is currently,

        int process_madvise(idtype_t idtype, id_t id, void *addr,
                size_t length, int advice, unsigned long flags);

@which is actually idtype_t for userspace libray and currently, it
supports P_PID and P_PIDFD.

What does "@which is actually idtype_t for userspace libray" mean?  Can
you clarify and expand?

Also, does this userspace library exist?  If so, where is it?

...