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Sun, 22 Mar 2026 22:32:25 +0100 (CET) Date: Sun, 22 Mar 2026 21:32:24 +0000 From: Josh Law To: SeongJae Park CC: akpm@linux-foundation.org, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: =?US-ASCII?Q?Re=3A_=5BPATCH_2/2=5D_mm/damon/core=3A_eliminate_hot-p?= =?US-ASCII?Q?ath_integer_division_in_damon=5Fmax=5Fnr=5Faccesses=28=29?= User-Agent: Thunderbird for Android In-Reply-To: <20260322213015.89161-1-sj@kernel.org> References: <20260322213015.89161-1-sj@kernel.org> Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-ZohoMailClient: External X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 36551A0002 X-Stat-Signature: qbiiruusbxaiirbq9k5yoje7hztftpqq X-HE-Tag: 1774215159-517026 X-HE-Meta: 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 Msa1aCYI 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 22 March 2026 21:30:15 GMT, SeongJae Park wrote: >On Sun, 22 Mar 2026 18:46:41 +0000 Josh Law w= rote: > >> Hardware integer division is slow=2E The function damon_max_nr_accesses= (), >> which is called very frequently (e=2Eg=2E, once per region per sample >> interval inside damon_update_region_access_rate), performs an integer >> division: attrs->aggr_interval / attrs->sample_interval=2E >>=20 >> However, the struct damon_attrs already caches this exact ratio in the >> internal field aggr_samples (since earlier commits)=2E We can eliminate >> the hardware division in the hot path by simply returning aggr_samples= =2E >>=20 >> This significantly reduces the CPU cycle overhead of updating the acces= s >> rates for thousands of regions=2E >>=20 >> Signed-off-by: Josh Law >> --- >> include/linux/damon=2Eh | 3 +-- >> 1 file changed, 1 insertion(+), 2 deletions(-) >>=20 >> diff --git a/include/linux/damon=2Eh b/include/linux/damon=2Eh >> index 6bd71546f7b2=2E=2Efffdb08326a2 100644 >> --- a/include/linux/damon=2Eh >> +++ b/include/linux/damon=2Eh >> @@ -960,8 +960,7 @@ static inline bool damon_target_has_pid(const struc= t damon_ctx *ctx) >> static inline unsigned int damon_max_nr_accesses(const struct damon_at= trs *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); > >checkpatch gives below warning: > >WARNING: min() should probably be min_t(unsigned long, attrs->aggr_sample= s, UINT_MAX) >#39: FILE: include/linux/damon=2Eh:963: >+ return min(attrs->aggr_samples, (unsigned long)UINT_MAX); > >Can we use min_t() as suggested? > >Otherwise, this patch looks good to me=2E > > >Thanks, >SJ > >[=2E=2E=2E] On it! V/R Josh Law