In the olden days, the Linux enthusiasts would recommend that you should create a SWAP partition that has twice the size of your RAM. Nobody knew why, but it just a rule we all followed. In those days, computers had something like 32 MB of RAM. Using 64 MB of disk space as SWAP seemed OK.
Today I opened a complex diagram in PDF format, generated by a computer program, with the Ubuntu PDF reader, Evince. The last setting Evince used for that file was with a very high zoom level, and so Evince tried to render the PDF page with that zoom level. After a few seconds I lost control of the computer due to thrasing. How can this be? The software security guys keep a constant watch on program flaws that make DoS attacks possible when opening a malicious file. I have generated a DoS attack to myself?!
When I regained control of the computer I discovered I had 3 GB of swap space installed. When a program is buggy and tries to allocate huge chunks of memory, of course it will bring the system to its knees.
My solution: reduce the swap space to 512 MB. Now Evince just fails to allocate memory and does not render the page. But I regain control and can switch to a different zoom level and finally render my page. A lesson learnt.