[$] Improving hot-page detection and promotion

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