[PATCH v4 0/3] mm/damon: Introduce a huge page collapsing mechanism using auto tuning

[PATCH v4 0/3] mm/damon: Introduce a huge page collapsing mechanism using auto tuning

[SJ Park]

From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>

Overview
========
This patch set introduces a new autotuning which allows to collapse hot
regions into hugepages.

Motivation
==========
Since TLB is a bottleneck for many systems[1], a way to optimize TLB
misses (or hits) is to use huge pages. Unfortunately, using "always" in
THP leads to memory fragmentation and memory waste. For this reason,
most application guides and system administrators suggest to disable
THP.

Selective huge page collapse per process is possible using prctl and a
launcher. However, this does not solve the issue with hot region
detection.  Additionally, it the sysadmin should create a launcher that
uses PRCTL to enable THP for a particular process.

We can use the DAMON support for DAMOS_HUGEPAGE and DAMOS_COLLAPSE, to
target a certain process. DAMOS_COLLAPSE can also target the hot regions
in that process.

Still, there is an issue with the amount of huge page consumption. Since
huge pages can lead to memory fragmentation and waste, there should be a
way to limit the amount of huge page consumption. There is hugetlbfs,
but it requires changes to the application code or the use of
libhugetlbfs.

DAMON has now a way to autotune some of the variables and adjust quotas
automatically, so that DAMON is fired only under the right
circumstances.  It would be nice to have something similar, but for huge
pages.

Solution
========
A new autotuning quota goal[2], damos_hugepage_mem_bp, is introduced,
which checks the huge page consumption to total memory consumption. This
new quota mechanism reuses current autotuning architecture.

In order to test this new mechanism, a sample module[3] was created, but
not included in this patch series. To demonstrate the tool, damo user
space tool was modified[4], which sets up huge pages collapse
autotuning.

Benchmarks
==========
Setup: physical server with arm64 processor with 4 NUMA nodes, 1 TB RAM
and running mariaDB 10.5.29. Sysbench was used for the benchmark, with
20 tables and 3 million rows per table. The database was pinned to one
of the nodes, and the benchmark framework to a different node. No
network traffic involved in the benchmark.

Damo user space tool was forked and hugepage_mem_bp support added[4].

DAMON was lauched using this command line:

sudo ./damo start $(pidof mariadbd) \
--monitoring_nr_regions_range 10 1000 \
--monitoring_intervals 5000 100000 60000000 \
--damos_quota_time 0 --damos_quota_space 128000000 \
--damos_quota_interval 1000 \
--damos_quota_weights 0 1 1 \
--damos_quota_goal hugepage_mem_bp <target> \
--damos_quota_goal_tuner temporal \
--damos_apply_interval 50000 \
--damos_access_rate 0 max --damos_age 50 max \
--damos_action collapse --debug_damon

<target> was 1000 to taget 10% hugepage to total memory ratio, or 2500
to target 25%. Tuner was also tested with consistent and temporal.

Results
=======
After the last timestamp, there was no change in huge page use, and the
total huge page to memory consumption ratio barely moved.

hugepage_mem_bp: 1000
goal tuner: temporal

+-----------+----------------+----------------+----------------------+
| timestamp | total mem used | huge page used | percentage hugepage  |
+-----------+----------------+----------------+----------------------+
| 0         | 16945.04297    | 0              | 0                    |
| 7         | 17008.69531    | 74             | 0.435071583          |
| 8         | 17036.40234    | 194            | 1.138738074          |
| 9         | 17017.01563    | 314            | 1.845211916          |
| 10        | 17029.67969    | 434            | 2.548491856          |
| 61        | 17111.30859    | 584            | 3.412947623          |
| 120       | 17071.05859    | 694            | 4.065360072          |
| 180       | 17133.88281    | 804            | 4.692456513          |
| 203       | 17088.16406    | 916            | 5.360435426          |
| 204       | 17126.34766    | 1046           | 6.107548562          |
| 205       | 17093.84375    | 1176           | 6.879669764          |
| 206       | 17142.77734    | 1298           | 7.571701913          |
| 209       | 17149.17969    | 1686           | 9.831374041          |
| 210       | 17097.30859    | 1754           | 10.25892462          |
+-----------+----------------+----------------+----------------------+

hugepage_mem_bp: 1000
goal tuner: consistent

+-----------+----------------+----------------+----------------------+
| timestamp | total mem used | huge page used | percentage hugepage  |
+-----------+----------------+----------------+----------------------+
| 0         | 16955.24609    | 0              | 0                    |
| 34        | 17039.71875    | 106            | 0.622075995          |
| 78        | 17009.47656    | 554            | 3.257007927          |
| 90        | 17048.92188    | 596            | 3.495822225          |
| 150       | 17092.90625    | 706            | 4.130368409          |
| 180       | 17053.08984    | 764            | 4.480126517          |
| 233       | 17100.50391    | 1496           | 8.748280216          |
| 239       | 17098.89063    | 2216           | 12.95990511          |
| 240       | 17135.44531    | 2334           | 13.62088908          |
| 245       | 17132.55078    | 2932           | 17.11362212          |
| 246       | 17117.95313    | 3052           | 17.82923448          |
| 250       | 17163.12109    | 3532           | 20.57900763          |
+-----------+----------------+----------------+----------------------+

hugepage_mem_bp: 2500
goal tuner: temporal

+-----------+----------------+----------------+----------------------+
| timestamp | total mem used | huge page used | percentage hugepage  |
+-----------+----------------+----------------+----------------------+
| 0         | 17010.31641    | 0              | 0                    |
| 9         | 17063.6875     | 50             | 0.2930199            |
| 10        | 17051.75781    | 170            | 0.996964664          |
| 60        | 17133.85547    | 572            | 3.338419663          |
| 90        | 17192.07813    | 626            | 3.641211932          |
| 120       | 17221.44531    | 682            | 3.960178647          |
| 181       | 17199.76172    | 790            | 4.593086886          |
| 208       | 17222.77734    | 1206           | 7.002354939          |
| 214       | 17245.17969    | 1904           | 11.04076637          |
| 215       | 17240.45703    | 2024           | 11.73982799          |
| 220       | 17234.79688    | 2624           | 15.22501262          |
| 228       | 17222.83594    | 3584           | 20.80958103          |
| 231       | 17247.55469    | 3944           | 22.86700968          |
| 235       | 17229.37109    | 4424           | 25.67708349          |
+-----------+----------------+----------------+----------------------+

hugepage_mem_bp: 1000
goal tuner: consist

+-----------+----------------+----------------+----------------------+
| timestamp | total mem used | huge page used | percentage hugepage  |
+-----------+----------------+----------------+----------------------+
| 0         | 17125.85156    | 0              | 0                    |
| 38        | 17081.23438    | 76             | 0.444932716          |
| 39        | 17133.11719    | 196            | 1.143983304          |
| 40        | 17119.83984    | 316            | 1.84581166           |
| 60        | 17109.72656    | 554            | 3.237924335          |
| 90        | 17164.11328    | 628            | 3.65879664           |
| 180       | 17177.66016    | 792            | 4.610639591          |
| 220       | 17180.86719    | 1378           | 8.020549749          |
| 226       | 17187.82031    | 1980           | 11.51978531          |
| 233       | 17143.48438    | 2818           | 16.4377319           |
| 240       | 17137.38281    | 3656           | 21.33347921          |
| 250       | 17175.5        | 4856           | 28.27283049          |
| 260       | 17199.66406    | 6056           | 35.20999002          |
| 270       | 17203.98438    | 7254           | 42.16465118          |
| 275       | 17207.21875    | 7762           | 45.10897498          |
+-----------+----------------+----------------+----------------------+

More detailed tables are provided here[5]

From this, we can conclude that the huge page autotuner works fine,
achieving the target. When using consistent autotuner, it actually
over-achieves the target, which is expected, since quota esz_bp is not
set to 0 to cap the DAMOS policy.

Patches Sequence
================
Patch 1 -> Introduce DAMOS_QUOTA_HUGEPAGE_MEM_BP and autotuning
Patch 2 -> sysfs support for the new quota goal
Patch 3 -> Document hugepage_mem_bp parameter

[1] https://dl.acm.org/doi/pdf/10.1145/3307650.3322227
[2] https://lore.kernel.org/e67f05ad-dbb9-45e6-ba30-b167a99ac67d@huawei-partners.com
[3] https://lore.kernel.org/20260616150316.580819-3-gutierrez.asier@huawei-partners.com
[4] https://github.com/asierHuawei/damo/commit/79ae1a4ab1c012a7161db85a000d14f08fa36736
[5] https://lore.kernel.org/all/03f678dd-9ef3-4b97-b753-c2e4554c5159@huawei-partners.com/

Changes from previous versions
==============================
v3 -> v4
  - v3: https://lore.kernel.org/20260720120140.881468-1-gutierrez.asier@huawei-partners.com
  - Add R-b: from SJ.
  - Handle a per-cpu count race where free pages larger than total
    pages.
  - Return 10,000 as hugepage memory ratio for the racy corner case,
    instead of MAX_INT.
  - Wordsmith commit message.
  - Rebase to latest mm-new.
v2[6] -> v3
  - Reworked the cover letter to make more clean the intents, design
    choices and results.
  - Added a guard in damos_hugepage_mem_bp in order to avoid potential
    division by 0.[7]
  - Fixed a typo in the documentation.
v1[8] -> v2
  - Rebased onto updated mm-new
  - Removed the sample module altogether, since it will increase
    maintenance costs[9]
  - Document hugepage_mem_bp in design.rst

RFC 4[10] -> v1
  - Renamed config to SAMPLE_DAMON_HPAGE, file to hpage.c and functions
    to damon_sample_hpage_...
  - Make the module depend on TRANSPARENT_HUGEPAGE, since the module
    will need some THP functions anyway
  - Removed documentation, since this is just a sample module
  - Removed DAMOS_QUOTA_HUGEPAGE_MEM_BP from damos_sysfs_add_quota_score
  - Added a short description of the module in Kconfig

RFC 3[11] -> RFC 4
  - Simplified the module
  - Removed unnecessary parameters
  - Renamed DAMOS_QUOTA_HUGEPAGE_MEM_BP to unify the naming style
  - Switched to DAMOS_QUOTA_GOAL_TUNER_TEMPORAL
  - Updated the documentation
  - Removed new interface for context creation with DAMON_OPS_VADDR

RFC 2[12] -> RFC 3
  - Module moved to samples
  - Change autotune to monitor total memory and hugepage
  - Added performnace benchmarks to the cover letter
  - Bail out gracefully when trying to start disable the module after
    the monitored task exited. This issue was discovered by sashiko [13]
  - Fixed typos and added quota_sz to the documentation discovered by
    sashiko [14]

RFC 1[15] -> RFC 2
  - Rebased into mm-new
  - Use DAMOS_COLLAPSE instead of DAMOS_HUGEPAGE
  - Fixed an issue that returned silently an error when the PID didn't
    exist in the system.[16]

[6] https://lore.kernel.org/all/20260714150116.382521-1-gutierrez.asier@huawei-partners.com
[7] https://lore.kernel.org/all/20260715151615.99767-1-sj@kernel.org/
[8] https://lore.kernel.org/20260616150316.580819-1-gutierrez.asier@huawei-partners.com
[9] https://lore.kernel.org/20260618150806.4633-1-sj@kernel.org
[10] https://lore.kernel.org/20260611150244.3454699-1-gutierrez.asier@huawei-partners.com
[11] https://lore.kernel.org/20260604150338.501128-1-gutierrez.asier@huawei-partners.com
[12] https://lore.kernel.org/20260522145518.158910-1-gutierrez.asier@huawei-partners.com
[13] https://lore.kernel.org/20260522171210.900B11F00A3D@smtp.kernel.org
[14] https://lore.kernel.org/20260522171633.AAF5B1F000E9@smtp.kernel.org
[15] https://lore.kernel.org/20260430134139.2446417-1-gutierrez.asier@huawei-partners.com
[16] https://lore.kernel.org/all/20260430154338.E22E6C2BCB3@smtp.kernel.org/

Note to Andrew:
Footnote references 6-16 are only used for changelog.  Hence those can
be removed with changelog.

Asier Gutierrez (3):
  mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning
  mm/damon/sysfs: support hugepage_mem_bp quota goal metric
  Docs/mm/damon/design: Document hugepage_mem_bp target metric

 Documentation/mm/damon/design.rst |  2 ++
 include/linux/damon.h             |  2 ++
 mm/damon/core.c                   | 19 +++++++++++++++++++
 mm/damon/sysfs-schemes.c          |  4 ++++
 4 files changed, 27 insertions(+)


base-commit: 0ae786fcfff4cfea3290e16a65fe12f5c99a6d2f
-- 
2.47.3

[PATCH v4 1/3] mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning

[SJ Park]

From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>

Introduce DAMOS_QUOTA_HUGEPAGE_MEM_BP auto tuning. Add a new DAMOS quota
goal metric to measure the amount of huge page consumption to total
memory consumption ratio.

Vmstat may lag, which in some cases may lead to NR_FREE_PAGES being
greater than or equal to the amount of RAM in the system. A guard is
added to avoid the extremely unlikely case [1]. In the case, return 100%
(10000 bp).

[1] https://lore.kernel.org/all/20260715151615.99767-1-sj@kernel.org/

Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
Reviewed-by: SJ Park <sj@kernel.org>
Signed-off-by: SJ Park <sj@kernel.org>
---
 include/linux/damon.h |  2 ++
 mm/damon/core.c       | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 5607f98ec6306..310509455db13 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -153,6 +153,7 @@ enum damos_action {
  * @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).
+ * @DAMOS_QUOTA_HUGEPAGE_MEM_BP:	Huge page to total used memory ratio.
  * @NR_DAMOS_QUOTA_GOAL_METRICS:	Number of DAMOS quota goal metrics.
  *
  * Metrics equal to larger than @NR_DAMOS_QUOTA_GOAL_METRICS are unsupported.
@@ -167,6 +168,7 @@ enum damos_quota_goal_metric {
 	DAMOS_QUOTA_ACTIVE_MEM_BP,
 	DAMOS_QUOTA_INACTIVE_MEM_BP,
 	DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP,
+	DAMOS_QUOTA_HUGEPAGE_MEM_BP,
 	NR_DAMOS_QUOTA_GOAL_METRICS,
 };
 
diff --git a/mm/damon/core.c b/mm/damon/core.c
index a5ea3e61e7f41..3fa1b096c8330 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -3038,6 +3038,22 @@ static unsigned int damos_get_in_active_mem_bp(bool active_ratio)
 	return mult_frac(inactive, 10000, total);
 }
 
+static unsigned int damos_hugepage_mem_bp(void)
+{
+	unsigned long thp, total_pages, free_pages;
+
+	total_pages = totalram_pages();
+	free_pages = global_zone_page_state(NR_FREE_PAGES);
+
+	if (total_pages <= free_pages)
+		return 10000;
+
+	thp = global_node_page_state(NR_ANON_THPS) +
+				global_node_page_state(NR_SHMEM_THPS) +
+				global_node_page_state(NR_FILE_THPS);
+	return mult_frac(thp, 10000, total_pages - free_pages);
+}
+
 static void damos_set_quota_goal_current_value(struct damon_ctx *c,
 		struct damos *s, struct damos_quota_goal *goal)
 {
@@ -3074,6 +3090,9 @@ static void damos_set_quota_goal_current_value(struct damon_ctx *c,
 		goal->current_value = damos_get_node_eligible_mem_bp(c, s,
 				goal->nid);
 		break;
+	case DAMOS_QUOTA_HUGEPAGE_MEM_BP:
+		goal->current_value = damos_hugepage_mem_bp();
+		break;
 	default:
 		break;
 	}
-- 
2.47.3

Re: [PATCH v4 1/3] mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] Unbounded metric calculation due to vmstat drift can destabilize quota tuning.
- [High] Silent 32-bit integer overflow in `mult_frac()` during memory ratio calculation.
--

commit 59f2c739bce03363ce501965d6708d807908af18
Author: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
Date:   Mon Aug 31 14:47:28 2026 +0000

mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning

This commit introduces a new DAMOS quota goal metric,
DAMOS_QUOTA_HUGEPAGE_MEM_BP, to auto-tune quotas based on the ratio of huge
page consumption to total memory consumption. It includes a fallback
mechanism for situations where vmstat counters drift and report more free
pages than total RAM.

Link: https://lore.kernel.org/all/20260715151615.99767-1-sj@kernel.org/

[ ... ]

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 644daf5a16560..9c0e42a1d2cfc 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c

[ ... ]

> @@ -3007,6 +3007,22 @@ static unsigned int damos_get_in_active_mem_bp(bool active_ratio)
>  	return mult_frac(inactive, 10000, total);
>  }
>  
> +static unsigned int damos_hugepage_mem_bp(void)
> +{
> +	unsigned long thp, total_pages, free_pages;
> +
> +	total_pages = totalram_pages();
> +	free_pages = global_zone_page_state(NR_FREE_PAGES);
> +
> +	if (total_pages <= free_pages)
> +		return 10000;
> +
> +	thp = global_node_page_state(NR_ANON_THPS) +
> +				global_node_page_state(NR_SHMEM_THPS) +
> +				global_node_page_state(NR_FILE_THPS);
> +	return mult_frac(thp, 10000, total_pages - free_pages);

[Severity: High]
Could the independent vmstat counters drift enough to produce an
out-of-bounds ratio here?

Because NR_ANON_THPS, NR_SHMEM_THPS, NR_FILE_THPS, and NR_FREE_PAGES are
updated asynchronously across CPUs, they can drift in opposite directions.
On systems with high core counts, if the system's actual used memory is
low but the thp stat artificially drifts higher than the calculated used
memory (or used memory drifts toward zero), the calculated ratio could
vastly exceed 10,000 (100%).

Would this cause the DAMOS auto-tuning PID controller to calculate an
exponentially inflated goal score, ultimately crushing the tuning quota to
zero and paralyzing DAMON's actions?

[Severity: High]
Can this calculation silently overflow on 32-bit architectures?

The mult_frac macro evaluates an intermediate multiplication that retains
the 32-bit type of x. Both thp and total_pages are declared as unsigned
long.

On 32-bit architectures like ARM32 with LPAE (which supports Transparent
Hugepages and up to 1TB RAM), unsigned long is 32 bits. If THP consumption
exceeds 429,496 base pages (around 1.71 GB), the intermediate calculation
(thp * 10000) will wrap around U32_MAX.

For example, 2GB of THP on a 3GB system might falsely report a 9.4% ratio
instead of 66.6%. Will this cause DAMON to mis-tune memory limits due to a
highly truncated quota goal metric?

> +}
> +

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260831144732.80910-1-sj@kernel.org?part=1

Re: [PATCH v4 1/3] mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning

[SJ Park]

On Mon, 31 Aug 2026 18:16:31 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
> - [High] Unbounded metric calculation due to vmstat drift can destabilize quota tuning.
> - [High] Silent 32-bit integer overflow in `mult_frac()` during memory ratio calculation.
> --
> 
> commit 59f2c739bce03363ce501965d6708d807908af18
> Author: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> Date:   Mon Aug 31 14:47:28 2026 +0000
> 
> mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning
> 
> This commit introduces a new DAMOS quota goal metric,
> DAMOS_QUOTA_HUGEPAGE_MEM_BP, to auto-tune quotas based on the ratio of huge
> page consumption to total memory consumption. It includes a fallback
> mechanism for situations where vmstat counters drift and report more free
> pages than total RAM.
> 
> Link: https://lore.kernel.org/all/20260715151615.99767-1-sj@kernel.org/
> 
> [ ... ]
> 
> > diff --git a/mm/damon/core.c b/mm/damon/core.c
> > index 644daf5a16560..9c0e42a1d2cfc 100644
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> 
> [ ... ]
> 
> > @@ -3007,6 +3007,22 @@ static unsigned int damos_get_in_active_mem_bp(bool active_ratio)
> >  	return mult_frac(inactive, 10000, total);
> >  }
> >  
> > +static unsigned int damos_hugepage_mem_bp(void)
> > +{
> > +	unsigned long thp, total_pages, free_pages;
> > +
> > +	total_pages = totalram_pages();
> > +	free_pages = global_zone_page_state(NR_FREE_PAGES);
> > +
> > +	if (total_pages <= free_pages)
> > +		return 10000;
> > +
> > +	thp = global_node_page_state(NR_ANON_THPS) +
> > +				global_node_page_state(NR_SHMEM_THPS) +
> > +				global_node_page_state(NR_FILE_THPS);
> > +	return mult_frac(thp, 10000, total_pages - free_pages);
> 
> [Severity: High]
> Could the independent vmstat counters drift enough to produce an
> out-of-bounds ratio here?
> 
> Because NR_ANON_THPS, NR_SHMEM_THPS, NR_FILE_THPS, and NR_FREE_PAGES are
> updated asynchronously across CPUs, they can drift in opposite directions.
> On systems with high core counts, if the system's actual used memory is
> low but the thp stat artificially drifts higher than the calculated used
> memory (or used memory drifts toward zero), the calculated ratio could
> vastly exceed 10,000 (100%).
> 
> Would this cause the DAMOS auto-tuning PID controller to calculate an
> exponentially inflated goal score, ultimately crushing the tuning quota to
> zero and paralyzing DAMON's actions?

The tuning logic ensures the resulting quota is 1 byte in minimum 2x of current
quota in maximum.  So, it will be no real problem.

> 
> [Severity: High]
> Can this calculation silently overflow on 32-bit architectures?
> 
> The mult_frac macro evaluates an intermediate multiplication that retains
> the 32-bit type of x. Both thp and total_pages are declared as unsigned
> long.
> 
> On 32-bit architectures like ARM32 with LPAE (which supports Transparent
> Hugepages and up to 1TB RAM), unsigned long is 32 bits. If THP consumption
> exceeds 429,496 base pages (around 1.71 GB), the intermediate calculation
> (thp * 10000) will wrap around U32_MAX.
> 
> For example, 2GB of THP on a 3GB system might falsely report a 9.4% ratio
> instead of 66.6%. Will this cause DAMON to mis-tune memory limits due to a
> highly truncated quota goal metric?

Known low priority issue.

> 
> > +}
> > +
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260831144732.80910-1-sj@kernel.org?part=1


Thanks,
SJ

Re: [PATCH v4 1/3] mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning

[Lian Wang]

Hi SJ and Asier,

Thanks for working on this and for providing the server results.  I have two
questions about what hugepage_mem_bp is intended to represent.

> Introduce DAMOS_QUOTA_HUGEPAGE_MEM_BP auto tuning. Add a new DAMOS quota
> goal metric to measure the amount of huge page consumption to total
> memory consumption ratio.

First, NR_ANON_THPS tracks anonymous PMD mappings, while NR_SHMEM_THPS and
NR_FILE_THPS track PMD-mappable page-cache folios.  Therefore, splitting only
an anonymous PMD mapping can change hugepage_mem_bp without physically
splitting the folio.  Is the intended metric PMD-mapped memory or physical
large-folio memory?  Clarifying this and adding a mapping-only test may help.

Second, the metric is global while a DAMOS scheme can target one process.
THPs from other processes or NUMA nodes can satisfy the target or dilute the
monitored process's changes.  Is this intentional?  If so, documenting the
scope and testing a background THP workload may be useful.

The temporal results approach the 10% and 25% targets, while the consistent
results overshoot the 10% target to about 20% and 45%.  I would describe this
as control-response data.  TPS, latency, TLB, fragmentation and collapse CPU
data could further show the workload benefit and cost.

If I have misunderstood any of this, please feel free to ignore these
comments and correct me.

The enum, quota-goal wiring and sysfs exposure otherwise look consistent with
the existing DAMOS autotuning framework.  I consider the points above
follow-up questions about semantics and evaluation, rather than blockers for
this series.

For the series:

Reviewed-by: Lian Wang <lianux.mm@gmail.com>

Please feel free to Cc me on related follow-up patches.  I am happy to help
review the code.  Besides my own DAMON work, I have recently been reviewing
and learning from other DAMON and MM work, and I would be glad to continue.

Thanks,
Lian

Sent using hkml (https://github.com/sjp38/hackermail)

Re: [PATCH v4 1/3] mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning

[SJ Park]

Hi Lian,

On Tue,  1 Sep 2026 14:58:35 +0800 Lian Wang <lianux.mm@gmail.com> wrote:

> Hi SJ and Asier,
> 
> Thanks for working on this and for providing the server results.  I have two
> questions about what hugepage_mem_bp is intended to represent.
> 
> > Introduce DAMOS_QUOTA_HUGEPAGE_MEM_BP auto tuning. Add a new DAMOS quota
> > goal metric to measure the amount of huge page consumption to total
> > memory consumption ratio.
> 
> First, NR_ANON_THPS tracks anonymous PMD mappings, while NR_SHMEM_THPS and
> NR_FILE_THPS track PMD-mappable page-cache folios.  Therefore, splitting only
> an anonymous PMD mapping can change hugepage_mem_bp without physically
> splitting the folio.  Is the intended metric PMD-mapped memory or physical
> large-folio memory?  Clarifying this and adding a mapping-only test may help.

Good point.  I was just missing this.  So, hugepage_mem_bp is not accounting
anon mTHPs, right?  Since hugepage_mem_bp is for general hugepages, I think
this is better to be improved.  Seems using MTHP_STAT_NR_ANON that is exposed
as 'nr_anon' can be used?  Because this is an improvement rather than a fix of
a bug, I think doing this as either a followup or new version of this series
are ok.  Asier, what do you think?

> 
> Second, the metric is global while a DAMOS scheme can target one process.

Actually it can target multiple processes if those are in single DAMON context.

> THPs from other processes or NUMA nodes can satisfy the target or dilute the
> monitored process's changes.  Is this intentional?

I think it is intentional.  The user should have the control on collapsing
hugepages, or believe the uncontrolled collapse mechanisms.

> If so, documenting the
> scope and testing a background THP workload may be useful.

More documentation and testing are always welcome :)

> 
> The temporal results approach the 10% and 25% targets, while the consistent
> results overshoot the 10% target to about 20% and 45%.  I would describe this
> as control-response data.  TPS, latency, TLB, fragmentation and collapse CPU
> data could further show the workload benefit and cost.

Yes, those would be helpful.  That's not mandatory for this simple change in my
opinion, though.  I would let Asier decide whether and when to make and share
such data.

> 
> If I have misunderstood any of this, please feel free to ignore these
> comments and correct me.

Your comments are very helpful, thank you for your review and comments, Lian.

> 
> The enum, quota-goal wiring and sysfs exposure otherwise look consistent with
> the existing DAMOS autotuning framework.  I consider the points above
> follow-up questions about semantics and evaluation, rather than blockers for
> this series.

I agree.

> 
> For the series:
> 
> Reviewed-by: Lian Wang <lianux.mm@gmail.com>

Thank you!

> 
> Please feel free to Cc me on related follow-up patches.  I am happy to help
> review the code.  Besides my own DAMON work, I have recently been reviewing
> and learning from other DAMON and MM work, and I would be glad to continue.

I'm curious if you and general reviewers need or prefer to directly be Cc-ed.
I was naively thinking people can search and review DAMON patches by
subscribing to the mailing list or using the archives via lore.kernel.org like
tools.


Thanks,
SJ

[...]

Re: [PATCH v4 1/3] mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning

[Lian Wang]

Hi SJ,

> Seems using MTHP_STAT_NR_ANON that is exposed as 'nr_anon' can be used?

Thank you for the suggestion.  I will study MTHP_STAT_NR_ANON and nr_anon
further, and document what I find.  We can continue discussing it by email,
and I will be happy to review any follow-up or updated patches.

> I'm curious if you and general reviewers need or prefer to directly be Cc-ed.
> I was naively thinking people can search and review DAMON patches by
> subscribing to the mailing list or using the archives via lore.kernel.org like
> tools.

I subscribe to many mailing lists, including linux-mm and DAMON, and I also
follow patches through lore.  Direct Cc is not required, but I appreciate it
for DAMON-related patches.  Because I care deeply about DAMON, directly Cc-ed
messages are filtered into my important mailbox, so I can archive and review
them quickly.

I am very happy to contribute to DAMON, and I look forward to continuing our
discussions and reviews by email.

Thanks,
Lian

Re: [PATCH v4 1/3] mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning

[SJ Park]

On Wed,  2 Sep 2026 09:56:01 +0800 Lian Wang <lianux.mm@gmail.com> wrote:

> Hi SJ,
> 
> > Seems using MTHP_STAT_NR_ANON that is exposed as 'nr_anon' can be used?
> 
> Thank you for the suggestion.  I will study MTHP_STAT_NR_ANON and nr_anon
> further, and document what I find.  We can continue discussing it by email,
> and I will be happy to review any follow-up or updated patches.
> 
> > I'm curious if you and general reviewers need or prefer to directly be Cc-ed.
> > I was naively thinking people can search and review DAMON patches by
> > subscribing to the mailing list or using the archives via lore.kernel.org like
> > tools.
> 
> I subscribe to many mailing lists, including linux-mm and DAMON, and I also
> follow patches through lore.  Direct Cc is not required, but I appreciate it
> for DAMON-related patches.  Because I care deeply about DAMON, directly Cc-ed
> messages are filtered into my important mailbox, so I can archive and review
> them quickly.

Thank you so much for your interest in DAMON, Lian.  But, the problem is that
my memory is so bad. :'(

I am maintaing mm patches review status dashboard for people who want to find
patches that waiting for their review.  It also provides the review status for
each sub-mm components [2] including DAMON [3].  Maybe finding patches that
waiting for your review from the dashboard is also a way for you?

If having the mail directly in your important mailbox is what you need, I
believe adding mails filtering rule for DAMON patches wouldn't be that
difficult.  If you use hkml, it could also help you monitoring [4] those.

Yet another systematic and long term solution that I could suggest is keep
reviewing and posting DAMON patches one by one, build more tracked records and
trusts, eventually adding your name as DAMON reviewer or maintainer on the
MAINTAINERS file.  All patches sent with get_maintainers.pl will automatically
Cc you.  It would take time and require patience, though, of course.

> 
> I am very happy to contribute to DAMON, and I look forward to continuing our
> discussions and reviews by email.

I really appreciate your interest and contributions to DAMON.  I hope it to be
continued long term!

[1] https://github.com/sjp38/mm_git_dashboard
[2] https://github.com/sjp38/mm_git_dashboard/tree/master/summary/subsystem
[3] https://github.com/sjp38/mm_git_dashboard/tree/master/summary/subsystem/DAMON
[4] https://github.com/sjp38/hackermail/blob/master/USAGE.md#monitoring-mails


Thanks,
SJ

[...]

Re: [PATCH v4 1/3] mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning

[Gutierrez Asier]

Hi SJ and Lian,

On 9/1/2026 5:23 PM, SJ Park wrote:
> Hi Lian,
> 
> On Tue,  1 Sep 2026 14:58:35 +0800 Lian Wang <lianux.mm@gmail.com> wrote:
> 
>> Hi SJ and Asier,
>>
>> Thanks for working on this and for providing the server results.  I have two
>> questions about what hugepage_mem_bp is intended to represent.
>>
>>> Introduce DAMOS_QUOTA_HUGEPAGE_MEM_BP auto tuning. Add a new DAMOS quota
>>> goal metric to measure the amount of huge page consumption to total
>>> memory consumption ratio.
>>
>> First, NR_ANON_THPS tracks anonymous PMD mappings, while NR_SHMEM_THPS and
>> NR_FILE_THPS track PMD-mappable page-cache folios.  Therefore, splitting only
>> an anonymous PMD mapping can change hugepage_mem_bp without physically
>> splitting the folio.  Is the intended metric PMD-mapped memory or physical
>> large-folio memory?  Clarifying this and adding a mapping-only test may help.
> 
> Good point.  I was just missing this.  So, hugepage_mem_bp is not accounting
> anon mTHPs, right?  Since hugepage_mem_bp is for general hugepages, I think
> this is better to be improved.  Seems using MTHP_STAT_NR_ANON that is exposed
> as 'nr_anon' can be used?  Because this is an improvement rather than a fix of
> a bug, I think doing this as either a followup or new version of this series
> are ok.  Asier, what do you think?
Agree, I will submit a new patch to fix this behaviour and account for mTHP.

Lian, thanks a lot for the review and pointing this issue.>>
>> Second, the metric is global while a DAMOS scheme can target one process.
> 
> Actually it can target multiple processes if those are in single DAMON context.
> 
>> THPs from other processes or NUMA nodes can satisfy the target or dilute the
>> monitored process's changes.  Is this intentional?
> 
> I think it is intentional.  The user should have the control on collapsing
> hugepages, or believe the uncontrolled collapse mechanisms.
> 
>> If so, documenting the
>> scope and testing a background THP workload may be useful.
> 
> More documentation and testing are always welcome :)
> 
>>
>> The temporal results approach the 10% and 25% targets, while the consistent
>> results overshoot the 10% target to about 20% and 45%.  I would describe this
>> as control-response data.  TPS, latency, TLB, fragmentation and collapse CPU
>> data could further show the workload benefit and cost.
> 
> Yes, those would be helpful.  That's not mandatory for this simple change in my
> opinion, though.  I would let Asier decide whether and when to make and share
> such data.
The idea of this patch was to introduce auto tuning. I think I submitted thebenchmark results when I sent the DAMOS_COLLAPSE feature.

Anyway, it shouldn't take long for me to get more data. I think it may be useful
for people to know the actual results in real application.

SJ, what's the best place to publish all those data? I believe you have more
experience sharing this data and which platform is the most useful one.>>
>> If I have misunderstood any of this, please feel free to ignore these
>> comments and correct me.
> 
> Your comments are very helpful, thank you for your review and comments, Lian.
> 
>>
>> The enum, quota-goal wiring and sysfs exposure otherwise look consistent with
>> the existing DAMOS autotuning framework.  I consider the points above
>> follow-up questions about semantics and evaluation, rather than blockers for
>> this series.
> 
> I agree.
> 
>>
>> For the series:
>>
>> Reviewed-by: Lian Wang <lianux.mm@gmail.com>
> 
> Thank you!
> 
>>
>> Please feel free to Cc me on related follow-up patches.  I am happy to help
>> review the code.  Besides my own DAMON work, I have recently been reviewing
>> and learning from other DAMON and MM work, and I would be glad to continue.
> 
> I'm curious if you and general reviewers need or prefer to directly be Cc-ed.
> I was naively thinking people can search and review DAMON patches by
> subscribing to the mailing list or using the archives via lore.kernel.org like
> tools.
> 
> 
> Thanks,
> SJ
> 
> [...]

-- 
Asier Gutierrez
Huawei

Re: [PATCH v4 1/3] mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning

[SJ Park]

On Wed, 2 Sep 2026 18:03:39 +0300 Gutierrez Asier <gutierrez.asier@huawei-partners.com> wrote:

> Hi SJ and Lian,
> 
> On 9/1/2026 5:23 PM, SJ Park wrote:
> > Hi Lian,
> > 
> > On Tue,  1 Sep 2026 14:58:35 +0800 Lian Wang <lianux.mm@gmail.com> wrote:
> > 
[...]
> >> Second, the metric is global while a DAMOS scheme can target one process.
> > 
> > Actually it can target multiple processes if those are in single DAMON context.
> > 
> >> THPs from other processes or NUMA nodes can satisfy the target or dilute the
> >> monitored process's changes.  Is this intentional?
> > 
> > I think it is intentional.  The user should have the control on collapsing
> > hugepages, or believe the uncontrolled collapse mechanisms.
> > 
> >> If so, documenting the
> >> scope and testing a background THP workload may be useful.
> > 
> > More documentation and testing are always welcome :)
> > 
> >>
> >> The temporal results approach the 10% and 25% targets, while the consistent
> >> results overshoot the 10% target to about 20% and 45%.  I would describe this
> >> as control-response data.  TPS, latency, TLB, fragmentation and collapse CPU
> >> data could further show the workload benefit and cost.
> > 
> > Yes, those would be helpful.  That's not mandatory for this simple change in my
> > opinion, though.  I would let Asier decide whether and when to make and share
> > such data.
> The idea of this patch was to introduce auto tuning. I think I submitted thebenchmark results when I sent the DAMOS_COLLAPSE feature.
> 
> Anyway, it shouldn't take long for me to get more data. I think it may be useful
> for people to know the actual results in real application.
> 
> SJ, what's the best place to publish all those data? I believe you have more
> experience sharing this data and which platform is the most useful one.>>

I'm never an expert in visibility :)  But if I should recommend, I get three
places off the top of my head.

First, you could simply share the data with plain mail on DAMON and wider
kernel mailing lists like linux-mm@ and linux-kernel@.

Second, if the data is matured, sharing those in conferences like LPC,
OSSummit, FOSDEM or DAMON (nano) Conference would be nice.

Third, if you prefer text, LWN or personal blogs like medias could also be good
places.  I also maintain DAMON porject blog [1].  Kunwu and Lian actually
contributed an article to the blog before.  If you want to submit an article
there, let me know.

[1] https://damonitor.github.io/posts/
[2] https://damonitor.github.io/posts/tlb_flush_policy/


Thanks,
SJ

[...]

[PATCH v4 2/3] mm/damon/sysfs: support hugepage_mem_bp quota goal metric

[SJ Park]

From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>

DAMOS has a new autotune policy metric: DAMOS_QUOTA_HUGEPAGE_MEM_BP.
This patch exposes DAMOS_QUOTA_HUGEPAGE_MEM_BP through sysfs.

Add the "hugepage_mem_bp" to the sysfs-schemes interface.

Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
Reviewed-by: SJ Park <sj@kernel.org>
Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 32f495a96b17a..d9b81d7b5910e 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -1269,6 +1269,10 @@ struct damos_sysfs_qgoal_metric_name damos_sysfs_qgoal_metric_names[] = {
 		.metric = DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP,
 		.name = "node_eligible_mem_bp",
 	},
+	{
+		.metric = DAMOS_QUOTA_HUGEPAGE_MEM_BP,
+		.name = "hugepage_mem_bp",
+	},
 };
 
 static ssize_t target_metric_show(struct kobject *kobj,
-- 
2.47.3

Re: [PATCH v4 2/3] mm/damon/sysfs: support hugepage_mem_bp quota goal metric

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The new `hugepage_mem_bp` metric is missing from the sysfs selftests.
--

commit a2c5ad81dadcc820e74efd9d73c1f576bbe76457
Author: Asier Gutierrez <gutierrez.asier@huawei-partners.com>

mm/damon/sysfs: support hugepage_mem_bp quota goal metric

This commit introduces the new DAMOS_QUOTA_HUGEPAGE_MEM_BP autotune policy
metric. It also exposes this metric to userspace through the sysfs-schemes
interface by adding "hugepage_mem_bp" to the list of recognized metrics.

> diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
> index 32f495a96b17a..d9b81d7b5910e 100644
> --- a/mm/damon/sysfs-schemes.c
> +++ b/mm/damon/sysfs-schemes.c

[ ... ]

> @@ -1269,6 +1269,10 @@ struct damos_sysfs_qgoal_metric_name damos_sysfs_qgoal_metric_names[] = {
>  		.metric = DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP,
>  		.name = "node_eligible_mem_bp",
>  	},
> +	{
> +		.metric = DAMOS_QUOTA_HUGEPAGE_MEM_BP,
> +		.name = "hugepage_mem_bp",
> +	},

[Severity: Medium]
Should the new hugepage_mem_bp metric be added to the DAMON sysfs kselftest?

Looking at tools/testing/selftests/damon/sysfs.sh in test_goal(), it explicitly
validates all supported metric strings by writing them to the sysfs node:

    ensure_write_succ "$fpath" "node_eligible_mem_bp" "valid input"
    ensure_write_fail "$fpath" "foo" "invalid input"

Without adding hugepage_mem_bp to this selftest script, the new sysfs metric
is left without automated test coverage.

>  };
>  
>  static ssize_t target_metric_show(struct kobject *kobj,

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260831144732.80910-1-sj@kernel.org?part=2

Re: [PATCH v4 2/3] mm/damon/sysfs: support hugepage_mem_bp quota goal metric

[SJ Park]

On Mon, 31 Aug 2026 18:22:08 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] The new `hugepage_mem_bp` metric is missing from the sysfs selftests.
> --
> 
> commit a2c5ad81dadcc820e74efd9d73c1f576bbe76457
> Author: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> 
> mm/damon/sysfs: support hugepage_mem_bp quota goal metric
> 
> This commit introduces the new DAMOS_QUOTA_HUGEPAGE_MEM_BP autotune policy
> metric. It also exposes this metric to userspace through the sysfs-schemes
> interface by adding "hugepage_mem_bp" to the list of recognized metrics.
> 
> > diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
> > index 32f495a96b17a..d9b81d7b5910e 100644
> > --- a/mm/damon/sysfs-schemes.c
> > +++ b/mm/damon/sysfs-schemes.c
> 
> [ ... ]
> 
> > @@ -1269,6 +1269,10 @@ struct damos_sysfs_qgoal_metric_name damos_sysfs_qgoal_metric_names[] = {
> >  		.metric = DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP,
> >  		.name = "node_eligible_mem_bp",
> >  	},
> > +	{
> > +		.metric = DAMOS_QUOTA_HUGEPAGE_MEM_BP,
> > +		.name = "hugepage_mem_bp",
> > +	},
> 
> [Severity: Medium]
> Should the new hugepage_mem_bp metric be added to the DAMON sysfs kselftest?
> 
> Looking at tools/testing/selftests/damon/sysfs.sh in test_goal(), it explicitly
> validates all supported metric strings by writing them to the sysfs node:
> 
>     ensure_write_succ "$fpath" "node_eligible_mem_bp" "valid input"
>     ensure_write_fail "$fpath" "foo" "invalid input"
> 
> Without adding hugepage_mem_bp to this selftest script, the new sysfs metric
> is left without automated test coverage.

I'm working on this, and this shouldn't be a blocker of this series.

> 
> >  };
> >  
> >  static ssize_t target_metric_show(struct kobject *kobj,
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260831144732.80910-1-sj@kernel.org?part=2


Thanks,
SJ

[PATCH v4 3/3] Docs/mm/damon/design: Document hugepage_mem_bp target metric

[SJ Park]

From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>

Document hugepage_mem_bp metric exposed by sysfs.

Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
Reviewed-by: SJ Park <sj@kernel.org>
Signed-off-by: SJ Park <sj@kernel.org>
---
 Documentation/mm/damon/design.rst | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
index aed6cb1cf4831..a8c163475ef2b 100644
--- a/Documentation/mm/damon/design.rst
+++ b/Documentation/mm/damon/design.rst
@@ -713,6 +713,8 @@ mechanism tries to make ``current_value`` of ``target_metric`` be same to
   bp (1/10,000).
 - ``node_eligible_mem_bp``: Scheme target access pattern-eligible memory ratio
   of a node in bp (1/10,000).
+- ``hugepage_mem_bp``: Total huge page to total used memory ratio in bp
+  (1/10,000).
 
 ``nid`` is optionally required for ``node_mem_used_bp``, ``node_mem_free_bp``,
 ``node_memcg_used_bp``, ``node_memcg_free_bp`` and ``node_eligible_mem_bp`` to
-- 
2.47.3

Re: [PATCH v4 3/3] Docs/mm/damon/design: Document hugepage_mem_bp target metric

[Randy Dunlap]

Hi,

On 8/31/26 7:47 AM, SJ Park wrote:
> From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> 
> Document hugepage_mem_bp metric exposed by sysfs.
> 
> Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> Reviewed-by: SJ Park <sj@kernel.org>
> Signed-off-by: SJ Park <sj@kernel.org>
> ---
>  Documentation/mm/damon/design.rst | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
> index aed6cb1cf4831..a8c163475ef2b 100644
> --- a/Documentation/mm/damon/design.rst
> +++ b/Documentation/mm/damon/design.rst
> @@ -713,6 +713,8 @@ mechanism tries to make ``current_value`` of ``target_metric`` be same to
>    bp (1/10,000).
>  - ``node_eligible_mem_bp``: Scheme target access pattern-eligible memory ratio
>    of a node in bp (1/10,000).
> +- ``hugepage_mem_bp``: Total huge page to total used memory ratio in bp
> +  (1/10,000).
>  
>  ``nid`` is optionally required for ``node_mem_used_bp``, ``node_mem_free_bp``,
>  ``node_memcg_used_bp``, ``node_memcg_free_bp`` and ``node_eligible_mem_bp`` to

I've looked thru the entire design.rst file and cannot find anything telling
me (or anyone) what "bp" means.  Explain??

thanks.
-- 
~Randy

Re: [PATCH v4 3/3] Docs/mm/damon/design: Document hugepage_mem_bp target metric

[Randy Dunlap]

On 8/31/26 8:45 AM, Randy Dunlap wrote:
> Hi,
> 
> On 8/31/26 7:47 AM, SJ Park wrote:
>> From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
>>
>> Document hugepage_mem_bp metric exposed by sysfs.
>>
>> Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
>> Reviewed-by: SJ Park <sj@kernel.org>
>> Signed-off-by: SJ Park <sj@kernel.org>
>> ---
>>  Documentation/mm/damon/design.rst | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
>> index aed6cb1cf4831..a8c163475ef2b 100644
>> --- a/Documentation/mm/damon/design.rst
>> +++ b/Documentation/mm/damon/design.rst
>> @@ -713,6 +713,8 @@ mechanism tries to make ``current_value`` of ``target_metric`` be same to
>>    bp (1/10,000).
>>  - ``node_eligible_mem_bp``: Scheme target access pattern-eligible memory ratio
>>    of a node in bp (1/10,000).
>> +- ``hugepage_mem_bp``: Total huge page to total used memory ratio in bp
>> +  (1/10,000).
>>  
>>  ``nid`` is optionally required for ``node_mem_used_bp``, ``node_mem_free_bp``,
>>  ``node_memcg_used_bp``, ``node_memcg_free_bp`` and ``node_eligible_mem_bp`` to
> 
> I've looked thru the entire design.rst file and cannot find anything telling
> me (or anyone) what "bp" means.  Explain??

OK, I found it on the internet. I still think that it would be a
good idea to say "basis point" one time (the first time that it is used).


-- 
~Randy

Re: [PATCH v4 3/3] Docs/mm/damon/design: Document hugepage_mem_bp target metric

[SJ Park]

On Mon, 31 Aug 2026 13:00:26 -0700 Randy Dunlap <rdunlap@infradead.org> wrote:

> 
> 
> On 8/31/26 8:45 AM, Randy Dunlap wrote:
> > Hi,
> > 
> > On 8/31/26 7:47 AM, SJ Park wrote:
> >> From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> >>
> >> Document hugepage_mem_bp metric exposed by sysfs.
> >>
> >> Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> >> Reviewed-by: SJ Park <sj@kernel.org>
> >> Signed-off-by: SJ Park <sj@kernel.org>
> >> ---
> >>  Documentation/mm/damon/design.rst | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
> >> index aed6cb1cf4831..a8c163475ef2b 100644
> >> --- a/Documentation/mm/damon/design.rst
> >> +++ b/Documentation/mm/damon/design.rst
> >> @@ -713,6 +713,8 @@ mechanism tries to make ``current_value`` of ``target_metric`` be same to
> >>    bp (1/10,000).
> >>  - ``node_eligible_mem_bp``: Scheme target access pattern-eligible memory ratio
> >>    of a node in bp (1/10,000).
> >> +- ``hugepage_mem_bp``: Total huge page to total used memory ratio in bp
> >> +  (1/10,000).
> >>  
> >>  ``nid`` is optionally required for ``node_mem_used_bp``, ``node_mem_free_bp``,
> >>  ``node_memcg_used_bp``, ``node_memcg_free_bp`` and ``node_eligible_mem_bp`` to
> > 
> > I've looked thru the entire design.rst file and cannot find anything telling
> > me (or anyone) what "bp" means.  Explain??
> 
> OK, I found it on the internet. I still think that it would be a
> good idea to say "basis point" one time (the first time that it is used).

You are right, and I agree.  I will add that clarification before the next
merge window.

> 
> 
> -- 
> ~Randy


Thanks,
SJ

Re: [PATCH v4 3/3] Docs/mm/damon/design: Document hugepage_mem_bp target metric

[Gutierrez Asier]

On 9/1/2026 3:47 AM, SJ Park wrote:
> On Mon, 31 Aug 2026 13:00:26 -0700 Randy Dunlap <rdunlap@infradead.org> wrote:
Hi,
> 
>>
>>
>> On 8/31/26 8:45 AM, Randy Dunlap wrote:
>>> Hi,
>>>
>>> On 8/31/26 7:47 AM, SJ Park wrote:
>>>> From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
>>>>
>>>> Document hugepage_mem_bp metric exposed by sysfs.
>>>>
>>>> Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
>>>> Reviewed-by: SJ Park <sj@kernel.org>
>>>> Signed-off-by: SJ Park <sj@kernel.org>
>>>> ---
>>>>  Documentation/mm/damon/design.rst | 2 ++
>>>>  1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
>>>> index aed6cb1cf4831..a8c163475ef2b 100644
>>>> --- a/Documentation/mm/damon/design.rst
>>>> +++ b/Documentation/mm/damon/design.rst
>>>> @@ -713,6 +713,8 @@ mechanism tries to make ``current_value`` of ``target_metric`` be same to
>>>>    bp (1/10,000).
>>>>  - ``node_eligible_mem_bp``: Scheme target access pattern-eligible memory ratio
>>>>    of a node in bp (1/10,000).
>>>> +- ``hugepage_mem_bp``: Total huge page to total used memory ratio in bp
>>>> +  (1/10,000).
>>>>  
>>>>  ``nid`` is optionally required for ``node_mem_used_bp``, ``node_mem_free_bp``,
>>>>  ``node_memcg_used_bp``, ``node_memcg_free_bp`` and ``node_eligible_mem_bp`` to
>>>
>>> I've looked thru the entire design.rst file and cannot find anything telling
>>> me (or anyone) what "bp" means.  Explain??
>>
>> OK, I found it on the internet. I still think that it would be a
>> good idea to say "basis point" one time (the first time that it is used).
> 
> You are right, and I agree.  I will add that clarification before the next
> merge window.
> 
>>
>>
>> -- 
>> ~Randy
> 
> 
> Thanks,
> SJ

SJ, should I submit a new patch to fix design.rst?

-- 
Asier Gutierrez
Huawei

Re: [PATCH v4 3/3] Docs/mm/damon/design: Document hugepage_mem_bp target metric

[SJ Park]

On Tue, 1 Sep 2026 08:20:50 +0300 Gutierrez Asier <gutierrez.asier@huawei-partners.com> wrote:

> On 9/1/2026 3:47 AM, SJ Park wrote:
> > On Mon, 31 Aug 2026 13:00:26 -0700 Randy Dunlap <rdunlap@infradead.org> wrote:
> Hi,
> > 
> >>
> >>
> >> On 8/31/26 8:45 AM, Randy Dunlap wrote:
> >>> Hi,
> >>>
> >>> On 8/31/26 7:47 AM, SJ Park wrote:
> >>>> From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> >>>>
> >>>> Document hugepage_mem_bp metric exposed by sysfs.
> >>>>
> >>>> Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> >>>> Reviewed-by: SJ Park <sj@kernel.org>
> >>>> Signed-off-by: SJ Park <sj@kernel.org>
> >>>> ---
> >>>>  Documentation/mm/damon/design.rst | 2 ++
> >>>>  1 file changed, 2 insertions(+)
> >>>>
> >>>> diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
> >>>> index aed6cb1cf4831..a8c163475ef2b 100644
> >>>> --- a/Documentation/mm/damon/design.rst
> >>>> +++ b/Documentation/mm/damon/design.rst
> >>>> @@ -713,6 +713,8 @@ mechanism tries to make ``current_value`` of ``target_metric`` be same to
> >>>>    bp (1/10,000).
> >>>>  - ``node_eligible_mem_bp``: Scheme target access pattern-eligible memory ratio
> >>>>    of a node in bp (1/10,000).
> >>>> +- ``hugepage_mem_bp``: Total huge page to total used memory ratio in bp
> >>>> +  (1/10,000).
> >>>>  
> >>>>  ``nid`` is optionally required for ``node_mem_used_bp``, ``node_mem_free_bp``,
> >>>>  ``node_memcg_used_bp``, ``node_memcg_free_bp`` and ``node_eligible_mem_bp`` to
> >>>
> >>> I've looked thru the entire design.rst file and cannot find anything telling
> >>> me (or anyone) what "bp" means.  Explain??
> >>
> >> OK, I found it on the internet. I still think that it would be a
> >> good idea to say "basis point" one time (the first time that it is used).
> > 
> > You are right, and I agree.  I will add that clarification before the next
> > merge window.
> > 
> >>
> >>
> >> -- 
> >> ~Randy
> > 
> > 
> > Thanks,
> > SJ
> 
> SJ, should I submit a new patch to fix design.rst?

The lack of the clarification of 'bp' was introduced before this patch.  So I
don't think you should do that on your own.

Of course you could do if you want to.  But that should be a separate patch in
my opinion.  Let me know if you will.  Otherwise I will do.


Thanks,
SJ

[...]

Re: [PATCH v4 3/3] Docs/mm/damon/design: Document hugepage_mem_bp target metric

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] Integer overflow in `mult_frac` on 32-bit systems for memory exceeding ~1.75 GB of huge pages, resulting in incorrect DAMOS quota auto-tuning.
- [Medium] The newly introduced DAMOS quota goal metric 'hugepage_mem_bp' is not tested in the DAMON sysfs selftests.
--

commit 59f2c739bce03363ce501965d6708d807908af18
Author: Asier Gutierrez <gutierrez.asier@huawei-partners.com>

mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning

Introduce DAMOS_QUOTA_HUGEPAGE_MEM_BP auto tuning. Add a new DAMOS quota
goal metric to measure the amount of huge page consumption to total
memory consumption ratio.

Link: https://lore.kernel.org/all/20260715151615.99767-1-sj@kernel.org/

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 644daf5a16560..9c0e42a1d2cfc 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
[ ... ]
> @@ -3007,6 +3007,22 @@ static unsigned int damos_get_in_active_mem_bp(bool active_ratio)
>  	return mult_frac(inactive, 10000, total);
>  }
>  
> +static unsigned int damos_hugepage_mem_bp(void)
> +{
> +	unsigned long thp, total_pages, free_pages;
> +
> +	total_pages = totalram_pages();
> +	free_pages = global_zone_page_state(NR_FREE_PAGES);
> +
> +	if (total_pages <= free_pages)
> +		return 10000;
> +
> +	thp = global_node_page_state(NR_ANON_THPS) +
> +				global_node_page_state(NR_SHMEM_THPS) +
> +				global_node_page_state(NR_FILE_THPS);
> +	return mult_frac(thp, 10000, total_pages - free_pages);

[Severity: High]
Does this calculation overflow on 32-bit systems?

Since thp is an unsigned long, on a 32-bit architecture it is a 32-bit
integer. If the system has more than ~1.75 GB of huge pages (about 429,496
pages), the internal multiplication thp * 10000 will exceed 4,294,967,295
and wrap around.

This leads to an incorrect value being returned from mult_frac() and results
in incorrect DAMOS auto-tuning.

commit a2c5ad81dadcc820e74efd9d73c1f576bbe76457
Author: Asier Gutierrez <gutierrez.asier@huawei-partners.com>

mm/damon/sysfs: support hugepage_mem_bp quota goal metric

DAMOS has a new autotune policy metric: DAMOS_QUOTA_HUGEPAGE_MEM_BP.
This patch exposes DAMOS_QUOTA_HUGEPAGE_MEM_BP through sysfs.

> diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
> index 32f495a96b17a..d9b81d7b5910e 100644
> --- a/mm/damon/sysfs-schemes.c
> +++ b/mm/damon/sysfs-schemes.c
[ ... ]
> @@ -1269,6 +1269,10 @@ struct damos_sysfs_qgoal_metric_name damos_sysfs_qgoal_metric_names[] = {
>  		.metric = DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP,
>  		.name = "node_eligible_mem_bp",
>  	},
> +	{
> +		.metric = DAMOS_QUOTA_HUGEPAGE_MEM_BP,
> +		.name = "hugepage_mem_bp",
> +	},
>  };

[Severity: Medium]
Should there be an accompanying update to the selftests for this new sysfs
metric?

Currently, the hugepage_mem_bp metric is missing from the tests. For
example, in tools/testing/selftests/damon/sysfs.sh:test_goal(), the new
metric is not verified:

tools/testing/selftests/damon/sysfs.sh:test_goal() {
    ...
    ensure_write_succ "$fpath" "node_eligible_mem_bp" "valid input"
    ensure_write_fail "$fpath" "foo" "invalid input"
    ...
}

Running the sysfs.sh selftest will silently skip testing the new metric
because it wasn't added to the hardcoded list of valid inputs.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260831144732.80910-1-sj@kernel.org?part=3

Re: [PATCH v4 3/3] Docs/mm/damon/design: Document hugepage_mem_bp target metric

[SJ Park]

On Mon, 31 Aug 2026 18:35:58 +0000 sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
> - [High] Integer overflow in `mult_frac` on 32-bit systems for memory exceeding ~1.75 GB of huge pages, resulting in incorrect DAMOS quota auto-tuning.
> - [Medium] The newly introduced DAMOS quota goal metric 'hugepage_mem_bp' is not tested in the DAMON sysfs selftests.
> --
> 
> commit 59f2c739bce03363ce501965d6708d807908af18
> Author: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> 
> mm/damon: Introduce DAMOS_QUOTA_HUGEPAGE auto tuning
> 
> Introduce DAMOS_QUOTA_HUGEPAGE_MEM_BP auto tuning. Add a new DAMOS quota
> goal metric to measure the amount of huge page consumption to total
> memory consumption ratio.
> 
> Link: https://lore.kernel.org/all/20260715151615.99767-1-sj@kernel.org/
> 
> > diff --git a/mm/damon/core.c b/mm/damon/core.c
> > index 644daf5a16560..9c0e42a1d2cfc 100644
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> [ ... ]
> > @@ -3007,6 +3007,22 @@ static unsigned int damos_get_in_active_mem_bp(bool active_ratio)
> >  	return mult_frac(inactive, 10000, total);
> >  }
> >  
> > +static unsigned int damos_hugepage_mem_bp(void)
> > +{
> > +	unsigned long thp, total_pages, free_pages;
> > +
> > +	total_pages = totalram_pages();
> > +	free_pages = global_zone_page_state(NR_FREE_PAGES);
> > +
> > +	if (total_pages <= free_pages)
> > +		return 10000;
> > +
> > +	thp = global_node_page_state(NR_ANON_THPS) +
> > +				global_node_page_state(NR_SHMEM_THPS) +
> > +				global_node_page_state(NR_FILE_THPS);
> > +	return mult_frac(thp, 10000, total_pages - free_pages);
> 
> [Severity: High]
> Does this calculation overflow on 32-bit systems?
> 
> Since thp is an unsigned long, on a 32-bit architecture it is a 32-bit
> integer. If the system has more than ~1.75 GB of huge pages (about 429,496
> pages), the internal multiplication thp * 10000 will exceed 4,294,967,295
> and wrap around.
> 
> This leads to an incorrect value being returned from mult_frac() and results
> in incorrect DAMOS auto-tuning.

Known low priority issue.

> 
> commit a2c5ad81dadcc820e74efd9d73c1f576bbe76457
> Author: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> 
> mm/damon/sysfs: support hugepage_mem_bp quota goal metric
> 
> DAMOS has a new autotune policy metric: DAMOS_QUOTA_HUGEPAGE_MEM_BP.
> This patch exposes DAMOS_QUOTA_HUGEPAGE_MEM_BP through sysfs.
> 
> > diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
> > index 32f495a96b17a..d9b81d7b5910e 100644
> > --- a/mm/damon/sysfs-schemes.c
> > +++ b/mm/damon/sysfs-schemes.c
> [ ... ]
> > @@ -1269,6 +1269,10 @@ struct damos_sysfs_qgoal_metric_name damos_sysfs_qgoal_metric_names[] = {
> >  		.metric = DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP,
> >  		.name = "node_eligible_mem_bp",
> >  	},
> > +	{
> > +		.metric = DAMOS_QUOTA_HUGEPAGE_MEM_BP,
> > +		.name = "hugepage_mem_bp",
> > +	},
> >  };
> 
> [Severity: Medium]
> Should there be an accompanying update to the selftests for this new sysfs
> metric?
> 
> Currently, the hugepage_mem_bp metric is missing from the tests. For
> example, in tools/testing/selftests/damon/sysfs.sh:test_goal(), the new
> metric is not verified:
> 
> tools/testing/selftests/damon/sysfs.sh:test_goal() {
>     ...
>     ensure_write_succ "$fpath" "node_eligible_mem_bp" "valid input"
>     ensure_write_fail "$fpath" "foo" "invalid input"
>     ...
> }
> 
> Running the sysfs.sh selftest will silently skip testing the new metric
> because it wasn't added to the hardcoded list of valid inputs.

I'm working for it, separately.  No blocker.

> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260831144732.80910-1-sj@kernel.org?part=3


Thanks,
SJ

Re: [PATCH v4 0/3] mm/damon: Introduce a huge page collapsing mechanism using auto tuning

[SJ Park]

On Mon, 31 Aug 2026 07:47:27 -0700 SJ Park <sj@kernel.org> wrote:

> From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> 
> Overview
> ========
> This patch set introduces a new autotuning which allows to collapse hot
> regions into hugepages.

Sashiko found no blocker for this series.  Sashiko sent findings to damon@
mailing list [1], and I replied to all the comments.  Please read those for
details.

[1] https://lore.kernel.org/damon/


Thanks,
SJ

[...]