[$] Memory-management optimization with DAMON

To a great extent, memory management is based on making predictions: whichpages of memory will a given process need in the near future?Unfortunately, it turns out that predictions are hard, especially when theyare about future events. In the absence of useful information sent back fromthe future, memory-management subsystems are forced to rely on observationsof recent behavior and an assumption that said behavior is likelyto continue. The kernel's memory-management decisions areopaque to user space, though, and often result in less-than-optimalperformance. A pair of patch sets from SeongJae Park tries to make memory-usage patterns visible to user space, and to letuser space change memory-management decisions in response.