#!/usr/bin/env python3

from time import sleep, time
import os
from sys import stdout

mlockall = True

if mlockall:
    from ctypes import CDLL
    CDLL('libc.so.6').mlockall(3)

psi_path = '/proc/pressure/memory'

psi_support = os.path.exists(psi_path)

def rline1(path):
    """read 1st line from path."""
    with open(path) as f:
        for line in f:
            return line[:-1]

def psi_mem_some_avg_total():
    return float(rline1(psi_path).rpartition('=')[2])

avg_min_time = 1

if psi_support:
    ta0 = time()
    a0 = psi_mem_some_avg_total()

while True:

    if psi_support:

        ta1= time()
        dt = ta1 - ta0

        if dt >= avg_min_time:

            a1 = psi_mem_some_avg_total()
            avg = (a1 - a0) / (ta1 - ta0) / 10000

            print('avg time:', round(dt, 1))
            print('PSI mem avg:', round(avg, 2))
            print(rline1(psi_path), '\n')
            ta0 = ta1
            a0 = a1

    stdout.flush()
    sleep(0.1)