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Sun, 22 Mar 2026 22:43:26 +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 v3 2/2] mm/damon/core: eliminate hot-path integer division in damon_max_nr_accesses() Date: Sun, 22 Mar 2026 21:43:25 +0000 Message-Id: <20260322214325.260007-3-objecting@objecting.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260322214325.260007-1-objecting@objecting.org> References: <20260322214325.260007-1-objecting@objecting.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-ZohoMailClient: External X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 312B2180002 X-Stat-Signature: kpm4g1uzknhha5sows44b9ucemaeimtn X-Rspam-User: X-HE-Tag: 1774215818-496650 X-HE-Meta: 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 swojhzYo fbyAig8JlfUVYGxCoSalaeB94cpQWNKzFAW7aRHQQ6n8Lhmz6Ssz8CUYzwoTBuw4C9NYwl6jzPt1ZxMHlJmgcP8vtu9ttA0kdggU7Dyx4kuNXyXk29orH4Wb3hljkyODGQqFtOKOTCoI83I81vADSV1OoOYD7KurBdmUEZmEQQvYHsdjj1/zIvQ2LNMrUjd+0qJX+9niv7gNO/6U6kiBCJmxKvfgeYseeGBBd/llYqljT5Z0smYqkD9ee3R0fV6EDtN0hZq36zMYoMq8+hC2OZUAPDPRjGt7gUUMrOyEi/yrB5kM5Y5EydmyMJQV2p38ok00e7H1FcP+vXJgg0QClUcK+CozVMYxVnh9+kUjxk8Xpona36O7wlJRWVLLKaNYt66RLbDf+pJPSiv8= 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 (e.g., once per region per sample interval inside damon_update_region_access_rate), performs an integer division: attrs->aggr_interval / attrs->sample_interval. However, the struct damon_attrs already caches this exact ratio in the internal field aggr_samples (since earlier commits). We can eliminate the hardware division in the hot path by simply returning aggr_samples. This significantly reduces the CPU cycle overhead of updating the access rates for thousands of regions. Signed-off-by: Josh Law --- include/linux/damon.h | 3 +-- 1 file changed, 1 insertion(+), 2 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); } -- 2.34.1