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b=ESVkzhHw0s2qBTPVfEyF/jPjOX+JKGUFB47v8c78YsrlEtdX4+3//kpYIvSWvNl7m kNS8q5Kx4OFadZm/wdtDw8Ql755HvxiUI949gn8+rMy+af7fWGts3/8sMkjzyph6Z3 sRpj08NMY9XKUFqH9NHRhf/Qjbdys99kUGRQMXQhY6RIotJqoTTQfdKACgpD0m2yHb l9GJhMKUdGzs+N/9mg0nqCXJAVtBKSemJX20twrXm6L8ohkjIXqN6BfOGPHfqkK75e 1Pka7mi1nzq88ogt+z1ijBo2LwMLnvaWNM2zL6v7Fj/+mpdeYTRJ+kAuRaI0smBQIX +0Q5aZNvFdHpQ== 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 v1.2 1/7] mm/damon/core: remove comment and test for nr_to_bp() divide-by-zero Date: Tue, 7 Jul 2026 18:32:44 -0700 Message-ID: <20260708013252.95888-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260708013252.95888-1-sj@kernel.org> References: <20260708013252.95888-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: 8o9rxbm38ghouadzi5peeci67hotsiax X-Rspamd-Queue-Id: 37004180007 X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1783474379-50614 X-HE-Meta: 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 EBbPSL2o KVDWw32Kj1ZeHmc1eMyYORWHS4HWGK6ZrD6huQZ4rd+biC5rq7yP+bkbZKUzZSncJRxn7/JlTvBRaZtuTWP7XXkYK8Yscjba2OfLUOpH7J6lYiB5nJV+EydZBG8SVvKTFJfNRWHuJNiDaFHhHUROglIPb7BXWQnq5KvW805Ij/mI5+qcyjaJLCqPeimlFNT5I+Wi3diunlT4k03sUDZcK605YvO0+AAWj+S98pxkOcsp0VyehVhGtF10nnJkAz0VpzTNWb9TOQ9NRYRs4VN9Wz6Buew== 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 | 25 +++++++++---------------- 2 files changed, 10 insertions(+), 23 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..b2a280556b841 100644 --- a/mm/damon/tests/core-kunit.h +++ b/mm/damon/tests/core-kunit.h @@ -575,26 +575,20 @@ static void damon_test_set_regions(struct kunit *test) }, 3); } -static void damon_test_nr_accesses_to_accesses_bp(struct kunit *test) +static void damon_test_max_nr_accesses(struct kunit *test) { struct damon_attrs attrs = { - .sample_interval = 10, - .aggr_interval = ((unsigned long)UINT_MAX + 1) * 10 + .sample_interval = 0, + .aggr_interval = 0, }; - /* - * 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."); + /* Zero aggregation interval doesn't cause division by zero */ + KUNIT_EXPECT_EQ(test, damon_max_nr_accesses(attrs), 1); - KUNIT_EXPECT_EQ(test, damon_nr_accesses_to_accesses_bp(123, &attrs), 0); + /* Too large aggregation interval doesn't cause overflow */ + attrs.aggr_interval = (unsigned long)UINT_MAX + 1; + KUNIT_EXPECT_GE(test, damon_max_nr_accesses(attrs), 0); + KUNIT_EXPECT_LE(test, damon_max_nr_accesses(attrs), UINT_MAX); } static void damon_test_update_monitoring_result(struct kunit *test) @@ -1572,7 +1566,6 @@ 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