[PATCH v2] mm/damon/tests/core-kunit: improve nr_samples_per_aggr test isolation

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

Test the zero sample interval case with a non-zero aggregation
interval, and keep the zero/zero case to cover the zero-result
fallback.

Also make the overflow case use an explicit sample interval so that
it does not depend on the zero sample interval fallback.

Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
Reviewed-by: Lian Wang <lianux.mm@gmail.com>
---
Changes in v2:
- Use 0/0 for the zero-result case, consistent with damon_set_attrs().
- Update commit msg and add Reviewed-by tag.
- Link to v1: https://lore.kernel.org/damon/20260908063635.2208922-1-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..a47a5cdf285 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);
 
-	/* Zero aggregation interval doesn't cause division by zero */
+	/* Zero sample and aggregation intervals cover the zero-result fallback. */
+	attrs = (struct damon_attrs){
+		.sample_interval = 0,
+		.aggr_interval = 0,
+	};
 	KUNIT_EXPECT_EQ(test, damon_nr_samples_per_aggr(&attrs), 1);
 
 	/*
@@ -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