Accelerating the search for victims

[hakavlad]

I noticed that you use not optimal way to search victim:

        // proc contains lots of directories not related to processes,
        // skip them
        if (!isnumeric(d->d_name))
            continue;

I found best way to find PIDs in proc: just check /proc/*/exe existence. This way lets you to exclude zombies and kthreads. This way works about 30% faster in my experience: it reduces search time from 9 ms to 6 ms in nohang.

def get_pid_list():
    """
    Find pid list expect kthreads and zombies.
    """
    pid_list = []
    for pid in os.listdir('/proc'):
        if os.path.exists('/proc/' + pid + '/exe') is True:
            pid_list.append(pid)
    return pid_list

def get_non_decimal_pids():
    """
    Find non-decimal like 'self' and 'thread-self'.
    """
    non_decimal_list = []
    for pid in pid_list:
        if pid[0].isdecimal() is False:
            non_decimal_list.append(pid)
    return non_decimal_list

non_decimal_list = get_non_decimal_pids() # you should run it at startup

pid_list = get_pid_list()

if '1' in pid_list:
    pid_list.remove('1')

for i in non_decimal_list:
    pid_list.remove(i)

# now pid_list contains only real userspace processes

[hakavlad]

 // Killing the process may have failed because we are not running as root.

If you use the new method, processes with other uids will be invisible to the daemon. And the daemon will only kill processes with the same UID and will never fail if it is not running as root.

[rfjakob]

processes with other uids will be invisible to the daemon

Actually, I think this is a bug. If another user uses up the memory, all my processes will be killed!