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bh=lnuvGybt67fKfdFIPouSOwFAG9kGA6DmWroqEsHCBQs=; b=QsiOtcb6/eodUJIc8Xx88I7v8Ydfi1mpwDa4yGy2249kSh1cCi2Uv28r/iWTRXVZyMGznNiwHi8AKqZIbEhVaWUkc6PLOEfCxXm8Hp5FEZKLRPouhRRj4el4+g7DmtEdA7mHElLhJaG9ZTb0Z+T5MndpYU82UPlBZLKtkawQIGA= ARC-Authentication-Results: i=1; mx.zohomail.eu; dkim=pass header.i=objecting.org; spf=pass smtp.mailfrom=objecting@objecting.org; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1774366809; s=zmail; d=objecting.org; i=objecting@objecting.org; h=From:From:To:To:Cc:Cc:Subject:Subject:Date:Date:Message-Id:Message-Id:MIME-Version:Content-Transfer-Encoding:Reply-To; bh=lnuvGybt67fKfdFIPouSOwFAG9kGA6DmWroqEsHCBQs=; b=ApcTv89QuZolSgC985pWaNnS8UKQ1dYo6Olk+EijNpyJKeV/xjfwnd3xsXl0A/Y6 E5Ik3PWPmWRd2gFT0XBj+PeKwqeyuBGeYIqBwAc0rlC5mes1GFu4p3JCCMQxvpBYDOq Xv+X2sYT696aZezdivaxY3OOc/GWL2GGfkyqZZWQ= Received: by mx.zoho.eu with SMTPS id 1774366806625819.9630672140645; Tue, 24 Mar 2026 16:40:06 +0100 (CET) From: Josh Law To: sj@kernel.org, akpm@linux-foundation.org Cc: damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Josh Law Subject: [PATCH] mm/damon/core: eliminate hot-path integer division in damon_max_nr_accesses() Date: Tue, 24 Mar 2026 15:40:05 +0000 Message-Id: <20260324154005.83651-1-objecting@objecting.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-ZohoMailClient: External X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 584371C0005 X-Stat-Signature: oay1wdqjopcz4kzcatzma3dby4h6ey8u X-Rspam-User: X-HE-Tag: 1774366822-700875 X-HE-Meta: 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 C3EXBURr w2ZaIw9hogdSAXKsUMei/NfZyKFv1PbNjSjeCSGfMj84DI87ENXgwEPf3xyKJ/pOS54fjFGYnMdWOHIh+7cKV3+irVABdD33vQa5T7uQAR9ag4M+U3Agvk6Fd2d9cEkHLC9uqmSzbnLKNUVg9i6aw3NbPhpG9LZPrMb9Z4Yr24O8Mrr+gPuKsJRKR6+cUboPVBn4gA0DBVw5ic/FTKulLFbQFHqzy5KiwJ3S+KtUJ/SGU5FHGyE0+akggk6aEpuApA8eiE9HSC74voyY5uFcq9NV4CXfhvYztgbqJTRyKWdDeTyEJzOGcSTAZUWtL2U/losKnoeRaBSxFVCOdk7tYfPTUzsXI82izS4zepgxWWKkLv3ZBg1XSzDdn7s4QORbSfROaYm2R75HssSc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hardware integer division is slow. The function damon_max_nr_accesses(), which is called very frequently, performs an integer division. However, the struct damon_attrs already caches this exact ratio in the internal field aggr_samples. We can eliminate the hardware division in the hot path by simply returning aggr_samples. Signed-off-by: Josh Law --- include/linux/damon.h | 3 +-- mm/damon/core.c | 1 + mm/damon/tests/core-kunit.h | 16 ++++++++++++---- 3 files changed, 14 insertions(+), 6 deletions(-) diff --git a/include/linux/damon.h b/include/linux/damon.h index 6bd71546f7b2..438fe6f3eab4 100644 --- a/include/linux/damon.h +++ b/include/linux/damon.h @@ -960,8 +960,7 @@ static inline bool damon_target_has_pid(const struct damon_ctx *ctx) static inline unsigned int damon_max_nr_accesses(const struct damon_attrs *attrs) { /* {aggr,sample}_interval are unsigned long, hence could overflow */ - return min(attrs->aggr_interval / attrs->sample_interval, - (unsigned long)UINT_MAX); + return min_t(unsigned long, attrs->aggr_samples, UINT_MAX); } diff --git a/mm/damon/core.c b/mm/damon/core.c index b0ab0ee6eab9..59b709f04975 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -582,6 +582,7 @@ struct damon_ctx *damon_new_ctx(void) ctx->attrs.sample_interval = 5 * 1000; ctx->attrs.aggr_interval = 100 * 1000; ctx->attrs.ops_update_interval = 60 * 1000 * 1000; + ctx->attrs.aggr_samples = 20; ctx->passed_sample_intervals = 0; /* These will be set from kdamond_init_ctx() */ diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h index e86d4f4fe261..56d03ef6a5a4 100644 --- a/mm/damon/tests/core-kunit.h +++ b/mm/damon/tests/core-kunit.h @@ -416,6 +416,8 @@ static void damon_test_nr_accesses_to_accesses_bp(struct kunit *test) .aggr_interval = ((unsigned long)UINT_MAX + 1) * 10 }; + attrs.aggr_samples = attrs.aggr_interval / attrs.sample_interval; + /* * In some cases such as 32bit architectures where UINT_MAX is * ULONG_MAX, attrs.aggr_interval becomes zero. Calling @@ -434,7 +436,8 @@ static void damon_test_nr_accesses_to_accesses_bp(struct kunit *test) static void damon_test_update_monitoring_result(struct kunit *test) { struct damon_attrs old_attrs = { - .sample_interval = 10, .aggr_interval = 1000,}; + .sample_interval = 10, .aggr_interval = 1000, + .aggr_samples = 100,}; struct damon_attrs new_attrs; struct damon_region *r = damon_new_region(3, 7); @@ -446,19 +449,24 @@ static void damon_test_update_monitoring_result(struct kunit *test) r->age = 20; new_attrs = (struct damon_attrs){ - .sample_interval = 100, .aggr_interval = 10000,}; + .sample_interval = 100, .aggr_interval = 10000, + .aggr_samples = 100,}; damon_update_monitoring_result(r, &old_attrs, &new_attrs, false); KUNIT_EXPECT_EQ(test, r->nr_accesses, 15); KUNIT_EXPECT_EQ(test, r->age, 2); new_attrs = (struct damon_attrs){ - .sample_interval = 1, .aggr_interval = 1000}; + .sample_interval = 1, .aggr_interval = 1000, + .aggr_samples = 1000, + }; damon_update_monitoring_result(r, &old_attrs, &new_attrs, false); KUNIT_EXPECT_EQ(test, r->nr_accesses, 150); KUNIT_EXPECT_EQ(test, r->age, 2); new_attrs = (struct damon_attrs){ - .sample_interval = 1, .aggr_interval = 100}; + .sample_interval = 1, .aggr_interval = 100, + .aggr_samples = 100, + }; damon_update_monitoring_result(r, &old_attrs, &new_attrs, false); KUNIT_EXPECT_EQ(test, r->nr_accesses, 150); KUNIT_EXPECT_EQ(test, r->age, 20); -- 2.34.1