inotify-cgroup-mem.py

import os
import pyinotify


def get_current_memory_cgroup_path():
    try:
        with open("/proc/self/cgroup", "r") as f:
            for line in f:
                parts = line.strip().split(":")
                if len(parts) == 3 and parts[1] == "":
                    return os.path.join("/sys/fs/cgroup", parts[2].lstrip('/'), "memory.max")
    except FileNotFoundError:
        raise Exception("Could not find /proc/self/cgroup. Are you in a cgroup environment?")
    print("Could not detect memory cgroup path in cgroupv2.")


class MemoryMaxEventHandler(pyinotify.ProcessEvent):
    def __init__(self, memory_max_path):
        self.memory_max_path = memory_max_path

    def process_IN_MODIFY(self, event):
        """Handles the IN_MODIFY event."""
        with open(self.memory_max_path, 'r') as f:
            memory_max = f.read().strip()
            print(f"Memory Max: {memory_max} bytes")


def poll_memory_max():
    memory_max_path = get_current_memory_cgroup_path()
    if not memory_max_path:
        print("Memory cgroup path could not be determined.")
        return

    wm = pyinotify.WatchManager()
    handler = MemoryMaxEventHandler(memory_max_path)
    notifier = pyinotify.Notifier(wm, handler)

    print(f"Watching memory.max at {memory_max_path}")
    wm.add_watch(memory_max_path, pyinotify.IN_MODIFY)

    try:
        notifier.loop()
    finally:
        notifier.stop()


poll_memory_max()

$ python /tmp/inotify-cgroup-mem.py
Watching memory.max at /sys/fs/cgroup/user.slice/user-1000.slice/[email protected]/app.slice/tmux-spawn-27f038ab-a676-4225-b873-7e2c4a8d1508.scope/memory.max
Memory Max: max bytes
Memory Max: 107374182400 bytes
Memory Max: max bytes

# echo max >| /sys/fs/cgroup/user.slice/user-1000.slice/[email protected]/app.slice/tmux-spawn-27f038ab-a676-4225-b873-7e2c4a8d1508.scope/memory.max
# echo 100G >| /sys/fs/cgroup/user.slice/user-1000.slice/[email protected]/app.slice/tmux-spawn-27f038ab-a676-4225-b873-7e2c4a8d1508.scope/memory.max
# echo max >| /sys/fs/cgroup/user.slice/user-1000.slice/[email protected]/app.slice/tmux-spawn-27f038ab-a676-4225-b873-7e2c4a8d1508.scope/memory.max