[PATCH v3] mm/damon/tests/core-kunit: add test for unconditionally skipping the last region

[Liew Rui Yan <aethernet65535@gmail.com>]

Commit b3723b596b54 ("mm/damon/core: fix unconditionally skip last
region") fixed a minor bug.

Add a KUnit test case to cover this behavior and prevent regressions in
the future.

Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
---

Changes from v2:
- v2: https://lore.kernel.org/damon/20260925045350.66595-1-aethernet65535@gmail.com
- Change the commit message, mention the fix rather than the original
  bug.

Changes from v1 RESEND:
- v1 RESEND: https://lore.kernel.org/damon/20260919080453.628679-1-aethernet65535@gmail.com
- Drop braces for single line, as suggested [1] in coding-style.
- Set min_region_sz initial value to power-of-2 value, '1'.
- [1] https://docs.kernel.org/process/coding-style.html#placing-braces-and-spaces

Changes from v1:
- v1: https://lore.kernel.org/damon/20260831113735.3349-1-aethernet65535@gmail.com
- Resend since the dependent patch is merged into mm-new, that would
  help us getting AI review help.

---
 mm/damon/tests/core-kunit.h | 42 +++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index 4a536d41cdb2..f4237436e1b4 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -1632,6 +1632,47 @@ static void damon_test_rand(struct kunit *test)
 	}
 }
 
+static void damon_test_last_region_quota_reset(struct kunit *test)
+{
+	struct damos s = {0};
+	struct damon_target *t;
+	struct damon_region *r1, *r2;
+	unsigned long min_region_sz = 1;
+	bool skipped;
+
+	t = damon_new_target();
+	if (!t)
+		kunit_skip(test, "target alloc fail");
+
+	r1 = damon_new_region(0, 100);
+	if (!r1) {
+		damon_free_target(t);
+		kunit_skip(test, "region 1 alloc fail");
+	}
+	damon_add_region(r1, t);
+
+	r2 = damon_new_region(100, 200);
+	if (!r2) {
+		damon_free_target(t);
+		kunit_skip(test, "region 2 alloc fail");
+	}
+	damon_add_region(r2, t);
+
+	s.quota.charge_target_from = t;
+	s.quota.charge_addr_from = r1->ar.end;
+
+	skipped = damos_skip_charged_region(t, r2, &s, min_region_sz);
+
+	/* 'r2' is not processed, it should not skip */
+	KUNIT_EXPECT_EQ(test, skipped, false);
+
+	/* 'r2' is last region, it should reset charge_{target,addr}_from */
+	KUNIT_EXPECT_PTR_EQ(test, s.quota.charge_target_from, NULL);
+	KUNIT_EXPECT_EQ(test, s.quota.charge_addr_from, 0);
+
+	damon_free_target(t);
+}
+
 static struct kunit_case damon_test_cases[] = {
 	KUNIT_CASE(damon_test_target),
 	KUNIT_CASE(damon_test_regions),
@@ -1664,6 +1705,7 @@ static struct kunit_case damon_test_cases[] = {
 	KUNIT_CASE(damon_test_is_last_region),
 	KUNIT_CASE(damon_test_walk_control_obsolete),
 	KUNIT_CASE(damon_test_rand),
+	KUNIT_CASE(damon_test_last_region_quota_reset),
 	{},
 };
 
-- 
2.55.0