Re: [PATCH v9.2] mm/damon: add node_eligible_mem_bp goal metric

[SeongJae Park]

On Mon, 27 Apr 2026 20:05:20 -0700 Ravi Jonnalagadda <ravis.opensrc@xxxxxxxxx> wrote:

> 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.
> 
> Suggested-by: SeongJae Park <sj@xxxxxxxxxx>
> Signed-off-by: Ravi Jonnalagadda <ravis.opensrc@xxxxxxxxx>
> Reviewed-by: SeongJae Park <sj@xxxxxxxxxx>

So, this looks good to me.  I find no blocker [1] from Sashiko review, too.  I
added this to damon/next tree.  Unless others find concerns or this is added to
mm-new by Andrew soon, I will repost this for mm-new merge.

[1] https://lore.kernel.org/20260428035754.116202-1-sj@xxxxxxxxxx


Thanks,
SJ

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