The best way to "defrag" your swap file is to set it set it to minimum size = 0 & maximum size = 0 and then click the SET button. Reboot the system. Upon logging in, you will receive an error stating that the paging file is too small yadda yadda yadda... Go back in and set the minimum and maximum size to a static size (to help reduce future fragmentation) and reboot the system again, even if it does not prompt you to do so.
Swap/Paging file will be clean as a whistle then.
Jeff