> The OS should start swapping very early to avoid bursts of disk I/O and rendering the system unusable. I think you're talking about the I/O of paging dirty t

> The OS should start swapping very early to avoid bursts of disk I/O and rendering the system unusable. I think you're talking about the I/O of paging dirty things out, but I'm talking about the fact that some memory location is no longer present in RAM, so accessing it will take 10 ms or more to page in. The system is not only useless while actively swapping. It's useless after it has ever swapped, and you can only recover by disabling swap ("sudo swapoff -a") or rebooting.