I feel like the real metric is like to see from swap usage is: how much time did I spend waiting to swap-in a page, how much extra cache pages it gave me, and what's the cache hit ratio. If the big purpose is to allow those extra few pages to be available, then either it's worth doing or not - there should be an objective way to look at this. Unfortunately only the second and third part is easily available. The first... maybe via systemtap?