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I'm not > > > > understanding why it's worth altering the kernel to permit this little > > > > shortcut? > > > > > > In practice it adds quite a bit of overhead for something that whatever > > > mechanism is using the pidfd can avoid. > > > > > > It was specifically intended for a real case of utilising > > > process_madvise(), using the newly extended ability to batch _any_ > > > madvise() operations for the current process, like: > > > > > > if (process_madvise(PIDFD_SELF, iovec, 10, MADV_GUARD_INSTALL, 0)) { > > > ... error handling ... > > > } > > > > > > vs. > > > > > > pid_t pid = getpid(); > > > int pidfd = pidfd_open(pid, PIDFD_THREAD); > > > > > > if (pidfd < 0) { > > > ... error handling ... > > > } > > > > > > if (process_madvise(PIDFD_SELF, iovec, 10, MADV_GUARD_INSTALL, 0)) { > > > ... cleanup pidfd ... > > > ... error handling ... > > > } > > > > > > ... > > > > > > ... cleanup pidfd ... > > > > > > So in practice, it's actually a lot more ceremony and noise. Suren has been > > > working with this code in practice and found this to be useful. > > > > It's also nice to add that people on the libc/allocator side should > > also appreciate skipping pidfd_open's reliability concerns (mostly, > > that RLIMIT_NOFILE Should Not(tm) ever affect thread spawning or a > > malloc[1]). Besides the big syscall reduction and nice speedup, that > > is. > > > > [1] whether this is the already case is an exercise left to the > > reader, but at the very least we should not add onto existing problems > > Thanks. > > Could we please get all the above spelled out much more thoroughly in > the [0/n] description (aka Patch Series Sales Brochure)? Ack, will expand if there's a respin, or Christian - perhaps you could fold the above explanation into the cover letter? Intent is for Christian to take this in his tree (if he so wishes) to be clear! Cheers