[$] Proactively reclaiming idle memory

Shakeel Butt started his 2019 Linux Storage, Filesystem, and
Memory-Management Summit session by noting that memory makes up a big part
of the total cost of equipping a data center. As a result, data-center
operators try to make the best use of memory they can, generally
overcommitting it significantly. In this session, Butt described a scheme
in use at Google to try to improve memory utilization; while the need for
the described functionality was generally agreed upon, the developers in
the room were not entirely happy with the solution presented.