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b=OTULZxMfEQn9PVoLW7K0LXBdrVffjx1gNhhyW3+NznKze+5HFUHJN2WkiZ88U3gNu t/SgxHwrWR1J5EwcPtThlgYrTpcB6aFiZzf2uz6ai174I1mMRScq0U6Kk428/R+ycb 8xGIQ9fZHzrp5CNX74ystm9Eam57znEEi0KpgRTTbxvNeijCSWmAGu82ycX0722tat WHd2SlmWWTTZY5VJRXhWyjecYFMv8uuczxDCFZe1/yYttOXiEgcFOS3ZUc2nU8Yt1Q aG6vE5JxRAsCOS5eSgfaQJVg98ISJzs04KAwYQdbaz+urTkO0Hm3ZsQBUUC2xpt91i 56cNwutvguOpQ== From: SeongJae Park To: Andrew Morton Cc: Liew Rui Yan , SeongJae Park , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 1/3] mm/damon/ops-common: optimize damon_hot_score() using ilog2() Date: Thu, 2 Apr 2026 08:57:28 -0700 Message-ID: <20260402155733.77050-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260402155733.77050-1-sj@kernel.org> References: <20260402155733.77050-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 617C8140007 X-Stat-Signature: ph7x3c9mtisz1czrhz5ibne8agzxrpog X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1775145466-890496 X-HE-Meta: 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 HUEJV1yK xPFfbQeCXpU+UgChJt/RHRP2ACrL5L4bm/1uTIPl0JO4sAYOKru7ZEGuEUgXqCx+SglX/GmR3QLx15z9mtW/Xo82qiUSw5YiL4gPD/o6h4XEMYk5kSDZRbyBPW/2N6JMB5Achb0kf49u+Pr3VR1CIBPVqLIBuF8UtbNy74VLl7zNzy6COdA6AaKVaIamCpOBIv1fcmdpsqAFdhZ3gO8C8eZz05mcjz1hlMgXKkjNT/g/AmgVKBHb0BNH13wLOvVfbIIckKdkzxQu7L1F5hceyRZueJDPnsCFIUygBKXVZY1ygx5p8rpLdgCgrfBGSs24vv7cR Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Liew Rui Yan The current implementation of damon_hot_score() uses a manual for-loop to calculate the value of 'age_in_log'. This can be efficiently replaced by ilog2(), which is semantically more appropriate for calculating the logarithmic value of age. In a simulated-kernel-module performance test with 10,000,000 iterations, this optimization showed a significant reduction in latency (average latency reduced from ~12ns to ~1ns). Test results from the simulated-kernel-module: - ilog2: DAMON Perf Test: Starting 10000000 iterations ============================================= Total Iterations : 10000000 Average Latency : 1 ns P95 Latency : 41 ns P99 Latency : 41 ns --------------------------------------------- Range (ns) | Count | Percent --------------------------------------------- 0-19 | 0 | 0% 20-39 | 2625000 | 26% 40-59 | 7374000 | 73% 60-79 | 0 | 0% 80-99 | 0 | 0% 100+ | 1000 | 0% ============================================= - for-loop: DAMON Perf Test: Starting 10000000 iterations ============================================= Total Iterations : 10000000 Average Latency : 12 ns P95 Latency : 51 ns P99 Latency : 60 ns --------------------------------------------- Range (ns) | Count | Percent --------------------------------------------- 0-19 | 0 | 0% 20-39 | 0 | 0% 40-59 | 9862000 | 98% 60-79 | 135000 | 1% 80-99 | 1000 | 0% 100+ | 2000 | 0% ============================================= Full raw benchmark results can be found at [1]. [1] https://github.com/aethernet65535/damon-hot-score-fls-optimize/tree/master/result-raw Signed-off-by: Liew Rui Yan Reviewed-by: SeongJae Park Signed-off-by: SeongJae Park --- Changes from v2 (https://lore.kernel.org/20260320192020.33004-1-aethernet65535@gmail.com) - Rebased to latest mm-new. Changes from v1 (actually it was RFC) (https://lore.kernel.org/20260320072431.248235-1-aethernet65535@gmail.com) - Replace fls() with ilog2() per SeongJae Park's suggestion for better semantic clarity. - Move performance benchmark results into the commit message and add comparison between for-loop and ilog2. mm/damon/ops-common.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c index 8c6d613425c1..3a0ddc3ac719 100644 --- a/mm/damon/ops-common.c +++ b/mm/damon/ops-common.c @@ -117,9 +117,12 @@ int damon_hot_score(struct damon_ctx *c, struct damon_region *r, damon_max_nr_accesses(&c->attrs); age_in_sec = (unsigned long)r->age * c->attrs.aggr_interval / 1000000; - for (age_in_log = 0; age_in_log < DAMON_MAX_AGE_IN_LOG && age_in_sec; - age_in_log++, age_in_sec >>= 1) - ; + if (age_in_sec) + age_in_log = min_t(int, ilog2(age_in_sec) + 1, + DAMON_MAX_AGE_IN_LOG); + else + age_in_log = 0; + /* If frequency is 0, higher age means it's colder */ if (freq_subscore == 0) -- 2.47.3