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Sun, 22 Mar 2026 19:46:44 +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 Subject: [PATCH 2/2] mm/damon/core: eliminate hot-path integer division in damon_max_nr_accesses() Date: Sun, 22 Mar 2026 18:46:41 +0000 Message-Id: <20260322184641.251966-3-objecting@objecting.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260322184641.251966-1-objecting@objecting.org> References: <20260322184641.251966-1-objecting@objecting.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-ZohoMailClient: External X-Stat-Signature: 86pk7qtozggdma9a79m1gouf6rpkx1nx X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: 0079B4000A X-HE-Tag: 1774205228-638288 X-HE-Meta: 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 tGS/X+YA VaEojPCWjgNf5DFujMkmr0EtGP+w4nIXBvRX6BOJ+0OAS0H1Tfd7F03a6j3uyhbJKc44FONZEHFSzSvQkkCNCDIjSl9GwxfMJXSZIwzbrNothDGvS1hEegM7enzLl1zSlABKct+7twhCZRYnle9WAgdNvjdfkQ2ZCi8wfGNGvcJYG1gET4mXui7aBdpNgmGeZ8LPTPiBXlpc8Z+51LJHpsJ6Dh6+PcubvBLGU13UgmkBRVS2lPl7pnF+V2WgVsFJjA9Uua2LcyQDKCyRs8BmqGtmx7/S7Gm1lBfZ2teyl/ebb0m/WKFOGQKUdaRoY3abgIP8JiVdIK3QrMkCkEdZYJLOAfWfmshHNiIlkKe+/oKavGAE= 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..fffdb08326a2 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(attrs->aggr_samples, (unsigned long)UINT_MAX); } -- 2.34.1