Some questions related to virtual memory never seem to go away.

Here are some of my favorites that I just love getting asked at least once every couple weeks. (Despite not being a VM hacker).

• My computer is using N MB of swap space, and there's memory free! This sucks!
  
  To understand this, think about what happens to infrequently used pages of a process when there's memory pressure. The OS decided to use those pages of RAM for something more useful.
  
• My computer has N MB of swap space free, and my processes still get oom killed. the kernel is buggy!
  
  When something got oom-killed, you ran out of _memory_, not swap space, and there was nothing else that could be swapped out to free up memory.
  
• My computer had N MB of RAM free, and they still got oom killed! the kernel sucks!
  
  There are different zones of memory. Having hundreds of MB of HIGHMEM available is irrelevant if something really needs memory it can use for DMA (Which is a very tight resource).
  

And my all-time favorite..

• I run without any swapspace configured, and once my app that allocates hundreds of gigs of memory keeps getting oom-killed. How do I stop the kernel doing this.
  

Answers on a postcard for that one ...