Upstart Automatic Swap Recovery

recover-swap.conf.sh

# /etc/init/recover-swap.conf
# author: mike smullin <mike dot smullin at wildworks dot com>
# see also: http://askubuntu.com/a/90399
# usage: start recover-swap; tailf /var/log/upstart/recover-swap.log
#
# WARNING: it is a little bit dangerous to swapoff while your service is still running;
#   means OOM killer may come reap your process if it need to swap again while swapoff is going,
#   which does take over an hour in our case.
#

respawn
start on startup
stop on shutdown
script
log(){
  echo "`date --rfc-3339=ns` $1";
}
while true; do
  free_data="$(free)"
  mem_data="$(echo "$free_data" | grep 'Mem:')"
  free_mem="$(echo "$mem_data" | awk '{print $4}')"
  buffers="$(echo "$mem_data" | awk '{print $6}')"
  cache="$(echo "$mem_data" | awk '{print $7}')"
  total_free=$((free_mem + buffers + cache))
  used_swap="$(echo "$free_data" | grep 'Swap:' | awk '{print $3}')"
  
  log "Free: $total_free kB ($((total_free / 1024)) MB), Swap: $used_swap kB ($((used_swap / 1024)) MB)"
  if [ $used_swap -eq 0 ]; then
      log "No swap is in use. Will check later.";
  elif [ $used_swap -lt $total_free ]; then
      log "Swap in use, and enough free memory. Freeing swap...";
      swapoff -a; 
      swapon -a; 
      log "Done.";
  else
      log "Swap in use, but not enough free memory. Will try later.";
  fi  

  sleep 3600; # retry once an hour
done;
end script