In defence of swap: common misconceptions
Chris Down says (on anonymous, i.e. allocated memory pages):
"[...] Swap is a storage area for these seemingly "unreclaimable" pages that allows us to page them out to a storage device on demand. This means that they can now be considered as equally eligible for reclaim as their more trivially reclaimable friends, like clean file pages, allowing more efficient use of available physical memory.
Swap is primarily a mechanism for equality of reclamation, not for emergency "extra memory". Swap is not what makes your application slow – entering overall memory contention is what makes your application slow."