I tried to run systems without swap a few years ago. That wasn't a very good idea. Most applications are very generous in their memory usage (not to mention all

I tried to run systems without swap a few years ago. That wasn't a very good idea. Most applications are very generous in their memory usage (not to mention allocation, almost always insane), and normally those pages are swapped out never to be heard from again. So without swap performance suffers since less pages are available for cache. (And in virtual environments it gets even worse since the balloon driver isn't really that great.) I didn't have time to see it through and abandoned it. In light of that this recommendation from Red Hat is very interesting. Just a fifth of memory as swap is probably enough to get real world performance back, without getting completely stuck when something goes haywire. On large memory systems it should probably be even less.