zRAM for compressing pages

Since paging (or swapping) on disk was really slow as hell on my laptop (2GB of RAM) when I ran out of memory, I decided to use zRAM which will set up a compressed block device in RAM and use it as a swap space. And yes this can lead to better performances! Tested and approved! 🙂 (Compressed ratio is approximatively 3:1).

On Ubuntu you have a package which install an upstart job handling the setup of zRAM. It will automagically set the zRAM swap space.

  1. Optional, remove your disk swap space (swapoff -a for temporary) in your fstab.
  2. Install zram-config.
  3. The upstart job is launched and your zRAM swap is set!

On other distributions, you can do what the Ubuntu’s job do, it basically detect the number of threads, set x threads zRAM devices and use it as a swap space with a priority of 5:

  # load dependency modules
  NRDEVICES=$(grep -c ^processor /proc/cpuinfo | sed 's/^0$/1/')
  if modinfo zram | grep -q ' zram_num_devices:' 2>/dev/null; then
  elif modinfo zram | grep -q ' num_devices:' 2>/dev/null; then
    exit 1
  modprobe zram $MODPROBE_ARGS

  # Calculate memory to use for zram (1/2 of ram)
  totalmem=`free | grep -e "^Mem:" | sed -e 's/^Mem: *//' -e 's/  *.*//'`
  mem=$(((totalmem / 2 / ${NRDEVICES}) * 1024))

  # initialize the devices
  for i in $(seq ${NRDEVICES}); do
    DEVNUMBER=$((i - 1))
    echo $mem > /sys/block/zram${DEVNUMBER}/disksize
    mkswap /dev/zram${DEVNUMBER}
    swapon -p 5 /dev/zram${DEVNUMBER}