From nobody Fri Apr 3 08:34:57 2026 Received: from sender-of-o55.zoho.eu (sender-of-o55.zoho.eu [136.143.169.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 46D7A386C09 for ; Tue, 24 Mar 2026 15:40:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=136.143.169.55 ARC-Seal: i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774366827; cv=pass; b=cyNP/fG7i0AxkduufYAvXzCZmz4WP2gV1rN/uQPsu4uQvGctdBfBjwdwPp/VOmpfE9LZwcSJ6SYk6G6OTZvMVuGLk5KjZGds/H3jV5tMz7nz28aGivnI/p95tkhm7yLyvyy/v0K47dQ3x5vpb/cr1pTZJKFqjqazdP+ufargmmg= ARC-Message-Signature: i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774366827; c=relaxed/simple; bh=3RWlpXoM5RX8kE45d2aZfoJlNKfJYpXiwumbuWOewRQ=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=lS/JKozkS68vnu5mY3lIox9P6/qlJaoOWM8XLgnZ5q8+G7q11Qz/Bw5hNQlc+HW8gUeb/bR98AktYjEkST3J5VA13eU0SjXHfSQNvG8XzmyzbkwfXxOvcSDdL35K+hsjku6E9vzdismmSMi3PODvrbiC64cVnZD+Q88p4slpYIs= ARC-Authentication-Results: i=2; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=objecting.org; spf=pass smtp.mailfrom=objecting.org; dkim=pass (1024-bit key) header.d=objecting.org header.i=objecting@objecting.org header.b=ApcTv89Q; arc=pass smtp.client-ip=136.143.169.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=objecting.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=objecting.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=objecting.org header.i=objecting@objecting.org header.b="ApcTv89Q" ARC-Seal: i=1; a=rsa-sha256; t=1774366809; cv=none; d=zohomail.eu; s=zohoarc; b=PG+uUpA0fQD+DWxyX5gc5CFsJwS1CLZTBshjd8V1y2FbCkIbB6bClUessVUdFywKZ9RLA7qd0fus54lprO+Ak/X9wFKhPYHBcRevA6oPgiX0KU/L6D5Uo4qzIZdpiZ0xuEWhuVJXcsV+ibwc9YVA/lsu1OrMvvBzuKPihqp2jt0= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.eu; s=zohoarc; t=1774366809; h=Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:MIME-Version:Message-ID:Subject:Subject:To:To:Message-Id:Reply-To; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ZohoMailClient: External Content-Type: text/plain; charset="utf-8" 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 da= mon_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); } =20 =20 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 =3D 5 * 1000; ctx->attrs.aggr_interval =3D 100 * 1000; ctx->attrs.ops_update_interval =3D 60 * 1000 * 1000; + ctx->attrs.aggr_samples =3D 20; =20 ctx->passed_sample_intervals =3D 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(struc= t kunit *test) .aggr_interval =3D ((unsigned long)UINT_MAX + 1) * 10 }; =20 + attrs.aggr_samples =3D 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(struc= t kunit *test) static void damon_test_update_monitoring_result(struct kunit *test) { struct damon_attrs old_attrs =3D { - .sample_interval =3D 10, .aggr_interval =3D 1000,}; + .sample_interval =3D 10, .aggr_interval =3D 1000, + .aggr_samples =3D 100,}; struct damon_attrs new_attrs; struct damon_region *r =3D damon_new_region(3, 7); =20 @@ -446,19 +449,24 @@ static void damon_test_update_monitoring_result(struc= t kunit *test) r->age =3D 20; =20 new_attrs =3D (struct damon_attrs){ - .sample_interval =3D 100, .aggr_interval =3D 10000,}; + .sample_interval =3D 100, .aggr_interval =3D 10000, + .aggr_samples =3D 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); =20 new_attrs =3D (struct damon_attrs){ - .sample_interval =3D 1, .aggr_interval =3D 1000}; + .sample_interval =3D 1, .aggr_interval =3D 1000, + .aggr_samples =3D 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); =20 new_attrs =3D (struct damon_attrs){ - .sample_interval =3D 1, .aggr_interval =3D 100}; + .sample_interval =3D 1, .aggr_interval =3D 100, + .aggr_samples =3D 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); --=20 2.34.1