[CentOS] What is eating up Swap

> recently I noticed, that one of our webservers is using swap space,
> while there is plenty of physical ram available.
> 
> free -m
>              total       used       free     shared    buffers     
> cached
> Mem:          8118       2014       6103          0         85        
> 261
> -/+ buffers/cache:       1667       6450
> Swap:         8197         77       8119
> 
> 
> It's not that much, but why?
> 
> Any ideas how to debug that? Thanks for any hint and suggestion.


#!/bin/bash
# Get current swap usage for all running processes
# Erik Ljungstrom 27/05/2011
# Modified by Mikko Rantalainen 2012-08-09
# Pipe the output to "sort -nk3" to get sorted output
SUM=0
OVERALL=0
for DIR in `find /proc/ -maxdepth 1 -type d -regex "^/proc/[0-9]+"`
do
     PID=`echo $DIR | cut -d / -f 3`
     PROGNAME=`ps -p $PID -o comm --no-headers`
     for SWAP in `grep Swap $DIR/smaps 2>/dev/null | awk '{ print $2 }'`
     do
         let SUM=$SUM+$SWAP
     done
     if (( $SUM > 0 )); then
         echo "PID=$PID swapped $SUM KB ($PROGNAME)"
     fi
     let OVERALL=$OVERALL+$SUM
     SUM=0
done
echo "Overall swap used: $OVERALL KB"