linux-kernel - [RFC PATCH v2 0/2] mm: multi-gen LRU scanning for page promotion

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Message-ID: <20250910235121.2544928-1-kinseyho@google.com>
Date: Wed, 10 Sep 2025 16:51:19 -0700
From: Kinsey Ho <kinseyho@...gle.com>
To: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc: Jonathan.Cameron@...wei.com, dave.hansen@...el.com, gourry@...rry.net, 
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Subject: [RFC PATCH v2 0/2] mm: multi-gen LRU scanning for page promotion

This patch series introduces a software-based approach to identifying
hot pages for promotion in tiered memory systems, particularly those
leveraging CXL-attached memory, by utilizing the Multi-Generational
LRU (MGLRU) framework. This method is designed to complement
hardware-based hotness detection mechanisms like Intel PMU sampling, AMD
IBS, or dedicated CXL memory monitoring units, providing a more
comprehensive view of page access patterns, similar to kmmscand [1].

We propose to utilize MGLRU's existing infrastructure to provide hot
page information. A key benefit here is the reuse of the MGLRU page
table walk code, thus avoiding the overhead and duplication of effort
involved in implementing a separate page table scanning mechanism. The
working set reporting proposal [2] also reuses MGLRU's infrastructure,
but focuses on cold page detection. It provides its own aging daemon,
which could additionally provide hot page information by integrating
this proof-of-concept.

This series is based on and relies on [3] as the aggregation and
promotion engine to implement the promotion policies. This is still in
the RFC stage as a proof-of-concept and requires more rigorous testing.

---
v2: Fixed a correctness issue during page table walk, where, on resume,
one page found with the access-bit set was incorrectly not added to the
pghot data structure provided by [3].

v1: https://lore.kernel.org/linux-mm/20250324220301.1273038-1-kinseyho@google.com/
---

[1] [RFC PATCH V3 00/17] mm: slowtier page promotion based on PTE A bit
https://lore.kernel.org/linux-mm/20250814153307.1553061-1-raghavendra.kt@amd.com/

[2] [PATCH v4 0/9] mm: workingset reporting
https://lore.kernel.org/linux-mm/20241127025728.3689245-1-yuanchu@google.com/

[3] [RFC PATCH v2 0/8] mm: Hot page tracking and promotion infrastructure
https://lore.kernel.org/linux-mm/20250910144653.212066-1-bharata@amd.com/

Kinsey Ho (2):
  mm: mglru: generalize page table walk
  mm: klruscand: use mglru scanning for page promotion

 include/linux/mmzone.h |   5 ++
 mm/Kconfig             |   8 ++
 mm/Makefile            |   1 +
 mm/internal.h          |   4 +
 mm/klruscand.c         | 118 +++++++++++++++++++++++++++
 mm/vmscan.c            | 181 +++++++++++++++++++++++++++++++----------
 6 files changed, 272 insertions(+), 45 deletions(-)
 create mode 100644 mm/klruscand.c

-- 
2.51.0.384.g4c02a37b29-goog