[$] Improving hot-page detection and promotion

Tiered-memory systems feature multiple types of memory with varying
performance characteristics; on such systems, good performance depends on
keeping the most frequently used data in the fastest memory. Identifying
that data and placing it properly is a challenge that has kept developers
busy for years. Bharata Rao, presenting remotely during a
memory-management-track session at the 2025 Linux Storage, Filesystem,
Memory-Management, and BPF Summit, led a discussion on a potential solution he has recently
posted; Raghavendra K T was also named on the
session proposal. It seems likely, based on the discussion, that
developers working in this area will not run out of problems anytime soon.