AMD engineer Bharata Rao has posted the latest RFC patches for 'pghot', a proposed Linux kernel subsystem for hot-page tracking and promotion. The system unifies hot page detection from multiple sources, centralizes promotion logic, and consolidates independent page-access tracking across the kernel. It operates in two modes: a default mode using 1 byte per page record and a precision mode using 4 bytes, tracking access frequency, time, and NUMA node ID. Hot pages are flagged for migration via a ready bit, and per-lower-tier-node threads perform batched migrations on configurable intervals. Benchmarks on an AMD EPYC Zen 5 server with CXL and multiple memory tiers showed measurable time savings in both page promotion and mixed promotion/demotion scenarios.
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