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

[Kunwu Chan <kunwu.chan@gmail.com>]

On Tue,  8 Sep 2026 06:36:50 -0700 SJ Park <sj@kernel.org> wrote:

> 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?

Good point. 
I checked damon_set_attrs() as well, and the `sample_interval <= aggr_interval` 
constraint makes `0/0` the consistent boundary case here.

I'll update the second case accordingly.

Thanks,
KunWu

> 
> >  
> >  	/*
> > @@ -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
> 

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