This Bash script will display how much swap each process is using, in kB

swap.sh

#! /bin/bash
#
# swap.sh: Shows the swap usage of each process
# Author: Robert Love
# source: http://www.quora.com/How-can-you-determine-what-processes-are-using-swap-space

swap_total=0
for i in /proc/[0-9]*; do
  pid=$(echo $i | sed -e 's/\/proc\///g')
  swap_pid=$(cat /proc/$pid/smaps |
    awk 'BEGIN{total=0}/^Swap:/{total+=$2}END{print total}')
  if [ "$swap_pid" -gt 0 ]; then
    name=$(cat /proc/$pid/status | grep ^Name: |
      awk '{print $2}')
    echo "${name} (${pid}) ${swap_pid} kB"
    let swap_total+=$swap_pid
  fi
done
echo
echo "Total: ${swap_total} kB"