mm/damon: add node_eligible_mem_bp goal metric

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
60% of scheme-eligible memory on DRAM" using PA-mode DAMON schemes.

Rather than using absolute thresholds, this metric tracks the ratio of
memory that matches each scheme's access pattern filters on a target node,
enabling the quota system to automatically adjust migration aggressiveness
to maintain the desired distribution.

What This Metric Measures
=========================

node_eligible_mem_bp:
    scheme_eligible_bytes_on_node / total_scheme_eligible_bytes * 10000

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

For maintaining 60% of hot memory on DRAM (node 0) and 40% on CXL
(node 1):

    PULL scheme: migrate_hot to node 0
      goal: node_eligible_mem_bp, nid=0, target=6000
      addr filter: node 1 address range (only migrate FROM CXL)
      "Move hot pages to DRAM if less than 60% of hot data is in DRAM"

    PUSH scheme: migrate_hot to node 1
      goal: node_eligible_mem_bp, nid=1, target=4000
      addr filter: node 0 address range (only migrate FROM DRAM)
      "Move hot pages to CXL if less than 40% of hot data is in CXL"

Each scheme independently measures its own eligible memory and adjusts its
quota to achieve its target ratio.  The schemes work in concert through
DAMON's unified monitoring context, with the quota autotuner balancing
their relative aggressiveness.

Implementation Details
======================

The implementation adds a new quota goal metric type
DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP to the existing DAMOS quota goal
framework.  When this metric is configured for a scheme:

1. During each quota adjustment cycle, damos_get_node_eligible_mem_bp()
   is called to calculate the current memory distribution.

2. The function iterates through all regions that match the scheme's
   access pattern (via __damos_valid_target()) and calculates:
   - Total eligible bytes across all nodes
   - Eligible bytes specifically on the target node (goal->nid)

3. For each eligible region, damos_calc_eligible_bytes() walks through
   the physical address range, using damon_get_folio() to look up
   each folio and determine its NUMA node via folio_nid().

4. Large folios are handled by calculating the exact overlap between
   the region boundaries and folio boundaries, ensuring accurate
   byte counts even when regions partially span folios.

5. The ratio (node_eligible / total_eligible * 10000) is returned
   as basis points, which the quota autotuner uses to adjust the
   scheme's effective quota size (esz).

The implementation requires CONFIG_DAMON_PADDR since damon_get_folio()
is only available for physical address space monitoring.

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.

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: This metric works with both TEMPORAL and CONSIST goal tuners.

Link: https://lore.kernel.org/20260428030520.701-1-ravis.opensrc@gmail.com
Signed-off-by: Ravi Jonnalagadda <ravis.opensrc@gmail.com>
Suggested-by: SeongJae Park <sj@kernel.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: Honggyu Kim <honggyu.kim@sk.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Yunjeong Mun <yunjeong.mun@sk.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/damon.h b/include/linux/damon.h
index f2cdb7c3f5e6..986b8c902585 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -159,6 +159,8 @@ enum damos_action {
  * @DAMOS_QUOTA_NODE_MEMCG_FREE_BP:	MemFree ratio of a node for a cgroup.
  * @DAMOS_QUOTA_ACTIVE_MEM_BP:		Active to total LRU memory ratio.
  * @DAMOS_QUOTA_INACTIVE_MEM_BP:	Inactive to total LRU memory ratio.
+ * @DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP:	Scheme-eligible memory ratio of a
+ *					node in basis points (0-10000).
  * @NR_DAMOS_QUOTA_GOAL_METRICS:	Number of DAMOS quota goal metrics.
  *
  * Metrics equal to larger than @NR_DAMOS_QUOTA_GOAL_METRICS are unsupported.
@@ -172,6 +174,7 @@ enum damos_quota_goal_metric {
 	DAMOS_QUOTA_NODE_MEMCG_FREE_BP,
 	DAMOS_QUOTA_ACTIVE_MEM_BP,
 	DAMOS_QUOTA_INACTIVE_MEM_BP,
+	DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP,
 	NR_DAMOS_QUOTA_GOAL_METRICS,
 };