[RFC PATCH v1.3 1/7] mm/damon/core: remove comment and test for nr_to_bp() divide-by-zero

[SJ Park <sj@kernel.org>]

The comments on damon_nr_accesses_to_accesses_bp() and its unit test
warn it can trigger division-by-zero when the aggregation interval is
zero.  Commit 35d4a3cf70a8 ("mm/damon/ops-common: handle extreme
intervals in damon_hot_score()") modified damon_nr_samples_per_aggr() to
always return non-zero.  Hence no division-by-zero of the note can
happen.  Remove the obsolete comment on the function.  The test code was
written to test the division-by-zero case, which cannot happen anymore.
Having it makes no sense.  Entirely remove the test code and its
comment.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/core.c             |  8 +-------
 mm/damon/tests/core-kunit.h | 23 -----------------------
 2 files changed, 1 insertion(+), 30 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 390e00b3685ef..a15005db82899 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -883,13 +883,7 @@ static unsigned int damon_accesses_bp_to_nr_accesses(
 	return accesses_bp * damon_max_nr_accesses(attrs) / 10000;
 }
 
-/*
- * Convert nr_accesses to access ratio in bp (per 10,000).
- *
- * Callers should ensure attrs.aggr_interval is not zero, like
- * damon_update_monitoring_results() does .  Otherwise, divide-by-zero would
- * happen.
- */
+/* Convert nr_accesses to access ratio in bp (per 10,000) */
 static unsigned int damon_nr_accesses_to_accesses_bp(
 		unsigned int nr_accesses, struct damon_attrs *attrs)
 {
diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index 0124f83b39b83..278d46632eff4 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -575,28 +575,6 @@ static void damon_test_set_regions(struct kunit *test)
 			}, 3);
 }
 
-static void damon_test_nr_accesses_to_accesses_bp(struct kunit *test)
-{
-	struct damon_attrs attrs = {
-		.sample_interval = 10,
-		.aggr_interval = ((unsigned long)UINT_MAX + 1) * 10
-	};
-
-	/*
-	 * In some cases such as 32bit architectures where UINT_MAX is
-	 * ULONG_MAX, attrs.aggr_interval becomes zero.  Calling
-	 * damon_nr_accesses_to_accesses_bp() in the case will cause
-	 * divide-by-zero.  Such case is prohibited in normal execution since
-	 * the caution is documented on the comment for the function, and
-	 * damon_update_monitoring_results() does the check.  Skip the test in
-	 * the case.
-	 */
-	if (!attrs.aggr_interval)
-		kunit_skip(test, "aggr_interval is zero.");
-
-	KUNIT_EXPECT_EQ(test, damon_nr_accesses_to_accesses_bp(123, &attrs), 0);
-}
-
 static void damon_test_update_monitoring_result(struct kunit *test)
 {
 	struct damon_attrs old_attrs = {
@@ -1572,7 +1550,6 @@ static struct kunit_case damon_test_cases[] = {
 	KUNIT_CASE(damon_test_split_above_half_progresses),
 	KUNIT_CASE(damon_test_ops_registration),
 	KUNIT_CASE(damon_test_set_regions),
-	KUNIT_CASE(damon_test_nr_accesses_to_accesses_bp),
 	KUNIT_CASE(damon_test_update_monitoring_result),
 	KUNIT_CASE(damon_test_set_attrs),
 	KUNIT_CASE(damon_test_mvsum),
-- 
2.47.3