According to my reading of the code, an open process file just holds a reference to a relatively lightweight handle to that process (struct pid), which means 1)

According to my reading of the code, an open process file just holds a reference to a relatively lightweight handle to that process (struct pid), which means 1) resource exhaustion by holding onto full process structures doesn't happen 2) numerical process ids can get recycled even if someone is holding a long-dead /proc/PID directory open for that pid, but the old opened directory keeps referring to the dead process.