Re: [PATCH] mm/damon/tests/core-kunit: improve nr_samples_per_aggr test isolation

[SJ Park <sj@kernel.org>]

Hi Kunwu,

On Tue,  8 Sep 2026 14:36:35 +0800 Kunwu Chan <kunwu.chan@gmail.com> wrote:

> The damon_nr_samples_per_aggr() test sets both intervals to zero,
> which exercises two different fallback paths at once.
> 
> Use separate compound initializers for each case so that each case
> tests one fallback path independently. Also make the overflow case
> use an explicit non-zero sample interval so that it does not depend
> on the zero sample interval fallback.

Thank you for sharing this patch!

> 
> Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
> ---
>  mm/damon/tests/core-kunit.h | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
> index c01e6a75cad..ff23208c181 100644
> --- a/mm/damon/tests/core-kunit.h
> +++ b/mm/damon/tests/core-kunit.h
> @@ -627,12 +627,20 @@ static void damon_test_set_regions(struct kunit *test)
>  
>  static void damon_test_nr_samples_per_aggr(struct kunit *test)
>  {
> -	struct damon_attrs attrs = {
> +	struct damon_attrs attrs;
> +
> +	/* Zero sample interval is treated as one. */
> +	attrs = (struct damon_attrs){
>  		.sample_interval = 0,
> -		.aggr_interval = 0,
> +		.aggr_interval = 5000,
>  	};
> +	KUNIT_EXPECT_EQ(test, damon_nr_samples_per_aggr(&attrs), 5000);

Thank you for adding this test case.

>  
> -	/* Zero aggregation interval doesn't cause division by zero */
> +	/* Zero samples per aggregation is treated as one. */
> +	attrs = (struct damon_attrs){
> +		.sample_interval = 5000,
> +		.aggr_interval = 0,
> +	};
>  	KUNIT_EXPECT_EQ(test, damon_nr_samples_per_aggr(&attrs), 1);

But damon_set_attrs() disallows sample intervals that are larger than the
aggregation intervals.  Hence this setup is somewhat unrealistic.  Should we
set sample_interval zero?

>  
>  	/*
> @@ -640,7 +648,10 @@ static void damon_test_nr_samples_per_aggr(struct kunit *test)
>  	 * overflow
>  	 */
>  	if (ULONG_MAX > UINT_MAX) {
> -		attrs.aggr_interval = (unsigned long)UINT_MAX + 1;
> +		attrs = (struct damon_attrs){
> +			.sample_interval = 1,
> +			.aggr_interval = (unsigned long)UINT_MAX + 1,
> +		};
>  		KUNIT_EXPECT_EQ(test, damon_nr_samples_per_aggr(&attrs),
>  				UINT_MAX);
>  	}
> 
> base-commit: d118502628f8b673be9023db8bdf878f64a7ed45
> -- 
> 2.43.0


Thanks,
SJ