[$] Working-set protection for anonymous pages

The kernel's memory-management subsystem goes to great lengths to keep thepages that are actually in use in memory. But sometimes it gets thingswrong, leading to reduced performance or, in the worst cases, flat-outthrashing. We may be about to see a significant improvement, though,thanks to apatch set from Joonsoo Kim changing how anonymous pages (thosecontaining data not backed by files on disk) are managed.As it turns out, all that had to be done was to make use of some work thatalready exists in related parts of the memory-management code.