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b=j9HcaiwgB8MPr5UR1dgiijiNs3I15Ty0podWkwwY8tMX1PP/G2F+OvXXl2BYTkMQA uvlMZKIDFVNG720KfYXuL7Nn9D5Sgty879SIN4iHD/KW0e0zbzsTh1i/lzrpJXHIbc 3/wYW1NZ8a21M7k3Pc6J3rYNewBc7jDwmpAe3F4R/4TDBwQESWYMfOrpyA/QkRUoYy /Aoj+836eszpmRXsTadmZEKKTFMQ7VPPfpK3/imVDZHq2rDNLWU/KBxIVywSKngI7a YV8cKCgrZ8bfx7FZIaT7NF/zvvEb/zHkDHtpu2GPw+6/b22+aKeMeW7Id/KAlSt/XJ qzw0byazU3WRQ== From: SeongJae Park To: Josh Law Cc: SeongJae Park , akpm@linux-foundation.org, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] mm/damon/core: eliminate hot-path integer division in damon_max_nr_accesses() Date: Sun, 22 Mar 2026 14:30:15 -0700 Message-ID: <20260322213015.89161-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260322184641.251966-3-objecting@objecting.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 718F0A0008 X-Stat-Signature: bohii8f1b6n5tboc6ad8ogcuesfc9ggk X-Rspam-User: X-HE-Tag: 1774215025-890575 X-HE-Meta: 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 6nPmic1t PEq8IyTx5hBAik0my1SIp1OiB4K5X0oVkeuhF71GmmrplTajvZw/yqkVcJxPgDwu6FnrxdM5l1Gtx+nvrnrIAPTpyeCdjxjh9kFnQ5IObU6ivs0WWjikgxRP9cMYo1Kb0SeNQiGa6vhmmihDEztmXJgBP90WQlNa/tczthPIzxPWy1sqARuVZwXberLED5WPb/s2g+Hbq+etSb3gv91thwbX1LH5swnQSi6igMJyHZb9uKpTyEbaR22b5l+FSXBjHe9VB1hyEMDQmNvEcDVXJC20HMoiNZQGdEI4r+F6CFJVGQeYxLLOKdv54Wg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 22 Mar 2026 18:46:41 +0000 Josh Law wrote: > 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); checkpatch gives below warning: WARNING: min() should probably be min_t(unsigned long, attrs->aggr_samples, UINT_MAX) #39: FILE: include/linux/damon.h:963: + return min(attrs->aggr_samples, (unsigned long)UINT_MAX); Can we use min_t() as suggested? Otherwise, this patch looks good to me. Thanks, SJ [...]