Re: [PATCH] mm/damon: make region calculations more precise

[SeongJae Park <sj@kernel.org>]

Hi Enze,

On Wed, 21 May 2025 15:07:47 +0800 Enze Li <lienze@kylinos.cn> wrote:

> The damon_sz_region() function misses counting one element when
> calculating region size, which leads to inaccurate results.  This patch
> corrects the size calculation by properly accounting for all elements.

Thank you for this patch, but I don't think the current calculation is wrong.
Please refer to the below comment.

> 
> Signed-off-by: Enze Li <lienze@kylinos.cn>
> ---
>  include/linux/damon.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index 47e36e6ea203..70473863f7fe 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -808,7 +808,7 @@ static inline struct damon_region *damon_first_region(struct damon_target *t)
>  
>  static inline unsigned long damon_sz_region(struct damon_region *r)
>  {
> -	return r->ar.end - r->ar.start;
> +	return r->ar.end - r->ar.start + 1;
>  }

'ar' here is 'struct damon_addr_range' which is for a half-open range.  Refer
to the comment on 'struct damon_addr_range' definition on include/linux/damon.h
for detail.  So I don't think the current calculation is wrong.

If you think this function also deserves a short comment for clarifying this,
your patch for that wil be welcomed :)

Please let me know if I'm missing something.


Thanks,
SJ

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