Re: [PATCH v1 2/3] mm/damon: introduce DAMON_HUGEPAGE for hot region hugepage collapsing

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
- [Medium] The `DAMOS_QUOTA_USER_INPUT` goal tuner feedback mechanism is statically stuck because `current_value` is never dynamically updated.
- [Medium] The scheme applies the DAMOS_COLLAPSE action to all regions including completely cold ones, contradicting the patch description.
- [Low] The module cannot be compiled due to a naming mismatch between the Kconfig symbol and the Makefile variable.
--

commit 7e15caa860a55beb8439fc6bb5f299c5c42fb138
Author: Asier Gutierrez <gutierrez.asier@huawei-partners.com>

mm/damon: introduce DAMON_HUGEPAGE for hot region hugepage collapsing

This patch introduces a new DAMON module (SAMPLE_DAMON_HPAGE)
which collapses hot regions into huge pages. The module monitors
a specific task using DAMON-based sampling and applies collapsing
based on memory usage.

> diff --git a/samples/damon/Makefile b/samples/damon/Makefile
> index 72f68cbf422aa..a348dc74ddcb1 100644
> --- a/samples/damon/Makefile
> +++ b/samples/damon/Makefile
> @@ -3,3 +3,4 @@
>  obj-$(CONFIG_SAMPLE_DAMON_WSSE) += wsse.o
>  obj-$(CONFIG_SAMPLE_DAMON_PRCL) += prcl.o
>  obj-$(CONFIG_SAMPLE_DAMON_MTIER) += mtier.o
> +obj-$(CONFIG_SAMPLE_DAMON_HUGEPAGE) += hpage.o

[Severity: Low]
Does this prevent the module from building? 

The Kconfig file defines the configuration option as SAMPLE_DAMON_HPAGE, 
but the Makefile evaluates CONFIG_SAMPLE_DAMON_HUGEPAGE. This mismatch 
means the build system might silently skip compiling hpage.o.

> diff --git a/samples/damon/hpage.c b/samples/damon/hpage.c
> new file mode 100644
> index 0000000000000..ebbe5e1be1a1d
> --- /dev/null
> +++ b/samples/damon/hpage.c

[ ... ]

> +	scheme = damon_new_scheme(&(struct damos_access_pattern) {
> +				.min_sz_region = HPAGE_PMD_SIZE,
> +				.max_sz_region = ULONG_MAX,
> +				.min_nr_accesses = 0,
> +				.max_nr_accesses = UINT_MAX,

[Severity: Medium]
Will this apply the collapse action to completely cold regions? 

The commit message states this module collapses "hot regions", but setting 
min_nr_accesses to 0 instructs DAMON to apply the action to all regions 
that meet the age threshold, including those with no accesses at all. 

Should this be set to a value strictly greater than 0 to only target 
heavily accessed regions?

[ ... ]

> +	if (quota_autotune_feedback) {
> +		goal = damos_new_quota_goal(DAMOS_QUOTA_USER_INPUT, 10000);
> +		if (!goal) {
> +			damon_destroy_ctx(ctx);
> +			return -ENOMEM;
> +		}
> +		goal->current_value = quota_autotune_feedback;
> +		damos_add_quota_goal(&scheme->quota, goal);
> +	}

[Severity: Medium]
Is there a missing mechanism to dynamically update this feedback value?

Since the module parameter is assigned to current_value exactly once at 
startup, without a dynamic update path while running, the auto-tuner will 
receive a constant error value. 

Won't this continuously push the quota aggressiveness in one direction 
until it hits the limits, rather than forming a proper feedback loop?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260616150316.580819-1-gutierrez.asier@huawei-partners.com?part=2