You do NOT want to utilize swap space if you care anything about performance. Your RAM is far, far too small for the processes that you are currently running. You need to at least double the amount of RAM you have. If that is not possible, you have to live with very bad performance, or reduce the size and/or number of processes running on your system.
When you use swap space, the performance can drop 50 to 200 times slower, a massive impact. Now if all your applications are interactive and users only talk to the programs once every few minutes, you won't see an impact. But if you have several programs running for long periods at the same, then the penalty for small RAM is enormous. You can see the page out rate by running vmstat -- look at the po column. If this is 1 digit (0-9), it is OK, 2 digits (10-99) means processes are starting to slow down, and more than 100 means your system is starved and cannot perform at all.
Here's what happens when two programs run at the same time but they won't fit into RAM:
1. process 1 is running and consuming 80% of RAM
2. process 2 has been waiting because it will not fit into the rest of memory. Process 1 is getting less important (because it is not allowing other processes to run) until finally, process 1 is deactivated.
3. The swap daemon starts removing memory pages from process 1 until there is enough room for process 2.
4. when process 2 has enough pages to run, it will start (or continue) running.
Now during the time page out is occurring, an enormous amount of time is wasted where neither process is running (paging is occurring). During this time, the kernel has to spinlock other processors because memory is being reorganized and this holds up kernel services.
You need a lot more RAM.
Bill Hassell, sysadmin
