First, bring up a terminal.
Applications > Accessories > Terminal
Then, in the window that comes up, type
sudo sysctl -w vm.swappiness=10
To make the change permanent, do the following:
in the terminal, type
sudo gedit /etc/sysctl.conf
(if you don't have gedit, type sudo apt-get install gedit, then perform the above step)
In the sysctl.conf file, add this line at the bottom of the page:
vm.swappiness=10
Afterwards, either click File > Save
Or just click the Save icon.
Close the window afterwards.
Congratulations! You just forced Linux to use the PS3's RAM more often instead of virtual RAM on the Hard Drive (known as swap file...it's 100 times slower than RAM access).