net.damacy.releasemem.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
  <dict>
    <key>Label</key>
    <string>net.damacy.releasemem</string>
    <key>ProgramArguments</key>
    <array>
      <string>/Users/jrollins/usr/bin/releasemem.py</string>
    </array>
    <key>StartInterval</key>
    <integer>60</integer>
    <key>Nice</key>
    <integer>20</integer>
    <key>LowPriorityIO</key>
    <true/>
  </dict>
</plist>

releasemem.py

#!/usr/bin/env python

import os
import re
import sys

from subprocess import call, Popen, PIPE

INACTIVE_THRESHOLD = 1024  # Number of MBs
FREE_THRESHOLD = INACTIVE_THRESHOLD / 2
RE_INACTIVE = re.compile('Pages inactive:\s+(\d+)')
RE_FREE = re.compile('Pages free:\s+(\d+)')
RE_SPECULATIVE = re.compile('Pages speculative:\s+(\d+)')
LOCK_FILE = '/var/tmp/releasemem.lock'


def acquire_lock():
    try:
        os.open(LOCK_FILE, os.O_CREAT | os.O_EXLOCK | os.O_NDELAY)
    except OSError:
        sys.exit('Could not acquire lock.')


def pages2mb(page_count):
    return int(page_count) * 4096 / 1024 ** 2


def free_inactive():
    vmstat = Popen('vm_stat', shell=True, stdout=PIPE).stdout.read()
    inactive = pages2mb(RE_INACTIVE.search(vmstat).group(1))
    free = pages2mb(RE_FREE.search(vmstat).group(1)) + \
            pages2mb(RE_SPECULATIVE.search(vmstat).group(1))
    return free, inactive


def main():
    acquire_lock()
    free, inactive = free_inactive()
    if (free < FREE_THRESHOLD) and (inactive > INACTIVE_THRESHOLD):
        print("Free: %dmb < %dmb" % (free, FREE_THRESHOLD))
        print("Inactive: %dmb > %dmb" % (inactive, INACTIVE_THRESHOLD))
        print('Purging...')
        call('/usr/bin/purge', shell=True)


if __name__ == '__main__':
    main()