drop_cache_if_idle

#!/usr/bin/env python3
#
# Drop the cache and inodes, if and only if the CPU usage is low
# Author: Mert Can Demir (validate)

import os
import psutil
import subprocess
import time

CPU_COUNT = os.cpu_count()
LOAD_THRESHOLD = (75 * CPU_COUNT) / 100


def root_check():
    if not os.geteuid() == 0:
        print("ERROR: Root access is not granted.")
        exit(1)


def load_check():
    print(f"INFO: The count of logical processors is {CPU_COUNT}")
    cpuload_all_cores = psutil.cpu_percent(percpu=True, interval=0.1)
    cpuload_core_max = max(cpuload_all_cores)

    cpuload_avg = psutil.cpu_percent(percpu=False, interval=0.1)
    load1m, _, _ = os.getloadavg()

    if cpuload_avg >= 10 or cpuload_core_max >= 30:
        print("INFO: CPU load detected, the command is not going to be executed.")
        return False
    elif load1m > LOAD_THRESHOLD:
        print("INFO: System load detected, the command is not going to be executed.")
        return False
    else:
        return True


def last_run_check():
    try:
        mod_time_since_epoch = os.path.getmtime("/run/drop_caches_last_run")
        current_time_since_epoch = time.time()
        last_run_time_in_seconds = current_time_since_epoch - mod_time_since_epoch
        print(
            f"INFO: The last run was before {round(last_run_time_in_seconds)} {'second' if round(last_run_time_in_seconds) <= 1 else 'seconds'}."
        )

    except OSError:
        print(
            "INFO: Path '/run/drop_caches_last_run' does not exists or is inaccessible. Continuing..."
        )
    except Exception as e:
        print(
            f"ERROR: The last run time of the command cannot be checked due to an unknown cause: {e}"
        )


def apply():
    try:
        out = subprocess.run(
            "sync; echo 3 > /proc/sys/vm/drop_caches; touch /run/drop_caches_last_run",
            shell=True,
        )
    except Exception as e:
        print(f"ERROR: The command cannot be executed due to an unknown cause: {e}")
        return False
    else:
        if isinstance(out, subprocess.CompletedProcess):
            print("INFO: No CPU load, the command is executed successfully.")
            return True
        else:
            print("ERROR: No CPU load, the command is not executed:")
            print(out)
            return False


def main():
    root_check()
    last_run_check()

    # Check load and execute if load is low
    if load_check():
        is_apply_succeed = apply()

        # Let's give the proper output to the user in case of failure
        if not is_apply_succeed:
            print("INFO: There was an error preventing the command being executed.")

    exit(0)


if __name__ == "__main__":
    main()