Using zram (formerly compcache) it is possible to slice a portion of the available RAM and create a compressed swap device that will eat some CPU cycles but will overall increase the amount of available RAM.

1. Copy the init script to /etc/init.d/zram.
2. Make the script executable with chmod +x /etc/init.d/zram.
3. Make the script start on boot using update-rc.d zram defaults.

zram

#!/bin/sh
 
### BEGIN INIT INFO
# Provides:          zram
# Required-Start:    $local_fs $syslog
# Required-Stop:     $local_fs $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Use compressed RAM as in-memory swap
# Description:       Use compressed RAM as in-memory swap
### END INIT INFO
 
# Author: Antonio Galea <antonio.galea@gmail.com>
# Thanks to Przemyslaw Tomczyk for suggesting swapoff parallelization
# Added LZ4 support, added restart suport
#    - Wizardry and Steamworks <office@grimore.org>
 
FRACTION=75
USE_LZ4=true
 
# Skip systemd redirect.
_SYSTEMCTL_SKIP_REDIRECT=OHYES
 
# Load the VERBOSE setting and other rcS variables
. /lib/init/vars.sh
 
# Define LSB log_* functions.
# Depend on lsb-base (>= 3.0-6) to ensure that this file is present.
. /lib/lsb/init-functions
 
MEMORY=`perl -ne'/^MemTotal:\s+(\d+)/ && print $1*1024;' < /proc/meminfo`
CPUS=`grep -c processor /proc/cpuinfo`
SIZE=$(( MEMORY * FRACTION / 100 / CPUS ))
 
case "$1" in
  "start")
    param=`modinfo zram|grep num_devices|cut -f2 -d:|tr -d ' '`
    modprobe zram $param=$CPUS
    for n in `seq $CPUS`; do
      i=$((n - 1))
      if [ $USE_LZ4 = "true" ]; then
          echo "lz4" > /sys/block/zram$i/comp_algorithm
      fi
      echo $SIZE > /sys/block/zram$i/disksize
      mkswap /dev/zram$i
      swapon /dev/zram$i -p 10
    done
    ;;
  "stop")
    for n in `seq $CPUS`; do
      i=$((n - 1))
      swapoff /dev/zram$i && echo "disabled disk $n of $CPUS" &
    done
    wait
    sleep .5
    modprobe -r zram
    ;;
  restart|reload|force-reload)
      ${0:-} stop
      ${0:-} start
    ;;
  *)
    echo "Usage: `basename $0` (start | stop)"
    exit 1
    ;;
esac

Alternatively, ZSWAP is a kernel space solution to compressing RAM.