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b=ZqriC04w3Ae7ID7pH6eyKY1qnkdT8nCo69YhVoPpjA4o6zWTh8u/iana8L6YTXxXS MV+s/CtR9xqcvu8lEavSitFKwh64iW1OSEu730zltUvFhiJhIuNeGeRtYJ2cdE2ZFa t9rDYSnk8NbyEpD9vxX9BBDJ4mCOFEYcJjE8L45qNjzibXSWcQhFFMyXq+0S45rZay Iz7zAkjqWW+onqp9r6m3cC0HjFGxWzlXP3QqtMQ2Or/LChU7487TfT9a4/t1MFDLjZ UmelNBlJdYMy2AD4RF9FvBK7vqU/kUeVaxkzNdmGehy2R0+YAdLzSGo8NbZrY9OdWi xkUK/GBpvmzrg== From: SJ Park To: Cc: SJ Park , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH v1.3 1/7] mm/damon/core: remove comment and test for nr_to_bp() divide-by-zero Date: Tue, 7 Jul 2026 19:48:47 -0700 Message-ID: <20260708024855.116614-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260708024855.116614-1-sj@kernel.org> References: <20260708024855.116614-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 027C2C0003 X-Stat-Signature: xp4iqnb4w5gng59ei8gzfb7prue5ztwh X-HE-Tag: 1783478944-678694 X-HE-Meta: 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 aZDTYGTd fdXgcslkXu66IHIKwbb7fHF07PZndyXU7wN75JOwE0f2s87fY9StjLiIe4P5+ep/rAcDiU/qrZCh05XzFkNUSa0Spk7SA7O9nGhLbtG6fn+8GzYBR//KGGAX1F0bf/IHSF/h1Jbm1XP2epQBUDp+GA3YrKJejMisfo4DtxYSb3hh9JjaHYm/2xJdUOrwK2iILpsUdy+sLRIcJDsVjbHA+TXymFUnbXIr938kG9iIobCZ9U3fjuR8RWnR3A39DYtKi6WsCXBa6ykrt3Dk0N649iieruA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 --- 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