Server :: Running Apache 2.2.3 - High Swap Usage

I am running Apache 2.2.3 on a CentOS release 5.3 (Final) with 100 Sites. I've notice that Apache is making my server Swap around 200 MBs.
"http://www.xxx.yyy.zzz/server-status" doesn't show me too much to, so I am looking the behavior of specific httpd process.
ProcessID "18753" is the one for "http://www.xxx.yyy.zzz/server-status" in my browser.

This command show me (In KBs) how much virtual memory is that specific process using:
# /etc/init.d/httpd start
# grep Private_Dirty /proc/18753/smaps | awk '{ print $2 }' | xargs ruby -e 'puts ARGV.inject { |i, j| i.to_i + j.to_i }'
3012
... Running this command a lot of times it gives me the same output, but suddenly...
# grep Private_Dirty /proc/18753/smaps | awk '{ print $2 }' | xargs ruby -e 'puts ARGV.inject { |i, j| i.to_i + j.to_i }'
21708

Something make that process (and all the others httpd process too) to use a lot more memory!

Part of my httpd.conf:
# Timeout 120
KeepAlive On
MaxKeepAliveRequests 100
KeepAliveTimeout 3

<IfModule prefork.c>
StartServers 5
MinSpareServers 5
MaxSpareServers 20
ServerLimit 256
MaxClients 256
MaxRequestsPerChild 100
</IfModule>

<IfModule worker.c>
StartServers 2
MaxClients 150
MinSpareThreads 25
MaxSpareThreads 75
ThreadsPerChild 25
MaxRequestsPerChild 0
</IfModule> #

My server is running Mysql 5.1.34, vsftpd 2.0.5, BIND 9.3.4-P1 (as slave). I couldn't found anything running in the specific time that httpd processes start to use that much memory.