mm/damon: add node_eligible_mem_bp and node_ineligible_mem_bp goal metrics

Changes since v5:
=================
https://lore.kernel.org/linux-mm/[email protected]/

- Rebased onto mm-new instead of damon/next for sashiko review
- Removed Reported-by/Closes tags per maintainer feedback (not needed for bugs found before merge)

Changes since v4:
=================
https://lore.kernel.org/linux-mm/[email protected]/

- Fixed commit message description for DAMOS_QUOTA_NODE_INELIGIBLE_MEM_BP per review feedback
- Added clarifying comment for ops-common.h include (for damon_get_folio())
- Fixed build error when CONFIG_DAMON_PADDR is disabled by adding #ifdef CONFIG_DAMON_PADDR guards around functions using damon_get_folio()
- Dropped RFC tag per maintainer feedback

This patch is based on top of mm-new.

Background and Motivation
=========================

In heterogeneous memory systems, controlling memory distribution across NUMA nodes is essential for performance optimization. This patch enables system-wide page distribution with target-state goals such as "maintain 30% of scheme-eligible memory on CXL" using PA-mode DAMON schemes.

What These Metrics Measure
==========================

node_eligible_mem_bp:
scheme_eligible_bytes_on_node / total_scheme_eligible_bytes * 10000

node_ineligible_mem_bp:

    (total - scheme_eligible_bytes_on_node) / total * 10000

These metrics are complementary: eligible_bp + ineligible_bp = 10000 bp.

Two-Scheme Setup for Hot Page Distribution
==========================================

For maintaining hot memory on DRAM (node 0) and CXL (node 1) in a 7:3 ratio:

    PUSH scheme: migrate_hot from node 0 -> node 1
      goal: node_ineligible_mem_bp, nid=0, target=3000
      "Move hot pages from DRAM to CXL if more than 70% of hot data is
       in DRAM"

    PULL scheme: migrate_hot from node 1 -> node 0
      goal: node_eligible_mem_bp, nid=0, target=7000
      "Move hot pages from CXL to DRAM if less than 70% of hot data is
       in DRAM"

The complementary goals create a feedback loop that converges to the target distribution.

Testing Results
===============

Functionally tested on a two-node heterogeneous memory system with DRAM (node 0) and CXL memory (node 1). A PUSH+PULL scheme configuration using migrate_hot actions was used to reach a target hot memory ratio between the two tiers. Testing used the TEMPORAL goal tuner available in damon/next and mm-unstable.

With the TEMPORAL tuner, the system converges quickly to the target distribution. The tuner drives esz to maximum when under goal and to zero once the goal is met, forming a simple on/off feedback loop that stabilizes at the desired ratio.

With the CONSIST tuner, the scheme still converges but more slowly, as it migrates and then throttles itself based on quota feedback. The time to reach the goal varies depending on workload intensity.

Note: These metrics work with both TEMPORAL and CONSIST goal tuners.

Ravi Jonnalagadda (1):
mm/damon: add node_eligible_mem_bp and node_ineligible_mem_bp goal
metrics

 include/linux/damon.h    |   6 ++
 mm/damon/core.c          | 188 ++++++++++++++++++++++++++++++++++++---
 mm/damon/sysfs-schemes.c |  12 +++
 3 files changed, 192 insertions(+), 14 deletions(-)

base-commit: b47b4fa4c232ee36aae58630e9d6520e35d33f3a

2.43.0