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b=ELVrL166n9hqhE3T/Pu9JB47LFzgNwWbtM+heqapekFShmlxAhZDkFKYf0uQEd0GD GY/OaKlRXMY/ncvggFCAio7fkpQrriF2IPx+sXyFLPDFXxRSp/6FzEKAKubJ9RxGN8 a5KVmtcc67tgBN6mx+gJ1I6nAhANxl96GkpU7ImxSX+kHb+PuQBi9hytRWRysT72Wn qCxCHOTl6NQKxm/4dSVL2OefVZgcdAymeEef9/iCZow+QjT11DlLg807UBtDoEmgBQ QNtdkilNaCBs3c+Rl6mzwedevJ5cAuWRam2n9IxW9kwo/SyvnPnj7jmAaj00vaOQXI rQqUe6tAQTsnw== From: SeongJae Park To: SeongJae Park Cc: Andrew Morton , Liew Rui Yan , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: (sashiko review) [PATCH 1/3] mm/damon/ops-common: optimize damon_hot_score() using ilog2() Date: Thu, 2 Apr 2026 17:16:57 -0700 Message-ID: <20260403001658.46229-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260402155733.77050-2-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: ib5tfmrkxxiigegchfey9zoz9kpuit1f X-Rspamd-Queue-Id: 02DD3C0008 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1775175420-123377 X-HE-Meta: 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 LrzfMTsE cvhjtNBaza7F9NTBrRSRLvmBFCgkmuww4QqF2F1c1BNgLezYkC8ypGst7ZRPW952ELT0B5I19yeV1052AUgG/OJxkOJmg3JOFIMMk3mHwzQU0WYgAwcAeH+S7KAu6rJyM4eCcAjTaoioMbrcEsS0SDrHcilMw0+5YfNPoRR0XmJ5icDbPIuppZu7qiLR/jhftBncrlVS2umRYgSBwQE8WKUggLkXFmp1ehp/YXO4xvvmiLkNN8GWr2HJm+5FmlOmRFSlF/l64te4UC54NQ5msegZyofUb37dznm1x5Hv7zP7Ed8UFZGLNL30LgLPP/cfz49kl9/D9TtTkKIxohEinaqS9ppBNLURsO9WT Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: TL; DR: sashiko didn't find a blocker for this patch. Forwarding Sashiko review in a review format with my inline comment, for sharing more details of my view and doing more discussions via mails if needed. > # review url: https://sashiko.dev/#/patchset/20260402155733.77050-2-sj@kernel.org > # start of sashiko.dev inline review > commit 3d1d9600685998aeba66926091d5a11897567bd0 > Author: Liew Rui Yan > > mm/damon/ops-common: optimize damon_hot_score() using ilog2() > > This commit replaces a manual for-loop with an ilog2() based calculation > to optimize the derivation of age_in_log in damon_hot_score(), improving > latency during performance tests. > > > diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c > > --- 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; > > This isn't a bug, but could this logic be simplified and the branch avoided > by using fls() instead of ilog2()? > > For non-constant variable arguments, ilog2(x) internally resolves to > fls(x) - 1. By evaluating ilog2(age_in_sec) + 1, this code essentially > calculates fls(age_in_sec) - 1 + 1. > > Since fls() natively returns 0 when the input is 0, using fls(age_in_sec) > directly would remove the need for the conditional branch entirely and > reduce the block to a single expression. We decided to use ilog2() since it makes the code easier to read in my taste. So, this is not a blocker for this patch. > > > # end of sashiko.dev inline review > # review url: https://sashiko.dev/#/patchset/20260402155733.77050-2-sj@kernel.org Thanks, SJ [...]