Question

(forgive my poor English, I am not native)

I tried Python resource module to limit child process.

It seems that setting RLIMIT_CPU can successfully limit the amount of cputime, but others like RLIMIT_RSS didn’t work at all.

For example, I use following script to call child.py, and set RSS limit to (1024, 1024):

import os
import sys
import resource
import subprocess

def setlimits():
    resource.setrlimit(resource.RLIMIT_RSS, (1024, 1024))

p = subprocess.Popen(["./child.py"], preexec_fn=setlimits)
print(p.wait())

child.py:

#!/usr/bin/env python3
import resource

print("RSS limit: ", resource.getrlimit(resource.RLIMIT_RSS))
a=[]
while True:
    a.append(1) # deadloop, until eat up memory

Child process print “RSS limit: (1024, 1024)” and then continue to run until killed.
I can see child.py eating my memory but RLIMIT_RSS didn’t work.

My OS is latest Archlinux (2.6.39 kernel), and Python is ver3.2.

Answer 1

According to the documentation for setrlimit(), RLIMIT_RSS has no effect in Linux 2.4.30 and later. Also, it only counts memory marked with madvise():

RLIMIT_RSS
Specifies the limit (in pages) of the process’s resident set (the number
of virtual pages resident in RAM).
This limit only has effect in Linux
2.4.x, x < 30, and there only affects calls to madvise() specifying
MADV_WILLNEED.

So, if you really want to limit processes this way, you’ll have to run a 2.4 kernel and hack the Python interpreter so it calls madvise() on allocated memory, which will probably have unexpected side-effects.