I was Looking at you laptops support sheet on the Toshiba Website:
http://www.toshiba.com/us/computers/laptops/satellite/L650/L655D-S5066
Under Performance and Graphics Memory I See this:
GRAPHICS MEMORY*
256MB-1917MB dynamically allocated shared graphics memory
I just subtracted the 1917 from your swap size and it gave me the memory amount of what your output showed. It may be that the graphics card is using this shared memory 100%. This may be due to the Normal ATI drive that would be in windows is not there to manage it.
I would reboot and go into your PC's BIOS. In there you may find a setting to turn of the shared Memory feature and just used the 256MB which should be more than enough to keep your system running smooth.
By default Ubuntu will use the open source Radeon driver for cards manufactured by AMD.
you may want to look at installing the Linux Driver for your Graphics card. Ubuntu has a Guide for this Here. https://help.ubuntu.com/community/BinaryDriverHowto/AMD
You simply need to open the setting menu for ubuntu, Click "Software & Updates".
Select the far right tab "Additional Drivers" and wait a few seconds for Ubuntu to build a list of drivers you can use.
It should looks something like this:
Note: I have an Nvidia GPU so you will see different drivers than me.
Make sure to pick the one that has the message (proprietary, Tested) next to it.
Once Selected click "Apply Changes" let it do its thing and reboot.