Re: [PATCH 2/2] mm/damon/core: eliminate hot-path integer division in damon_max_nr_accesses()

[SeongJae Park]

On Sun, 22 Mar 2026 18:46:41 +0000 Josh Law <objecting@xxxxxxxxxxxxx> 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 <objecting@xxxxxxxxxxxxx>
> ---
>  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

[...]