Re: [PATCH] mm/damon: increment pa_stat damon address range by folio size

[SeongJae Park <sj@kernel.org>]

Hi Usama,


Let's use "mm/damon/paddr: " prefix for the patch title, to be more consistent
with others.

On Mon, 13 Jan 2025 18:03:40 +0000 Usama Arif <usamaarif642@gmail.com> wrote:

> This is to take into account for folios with size > 1 page.
> Iterating at PAGE_SIZE increment would increment sz_filter_passed
> multiple times for the same folio by folio_size, providing incorrect
> stats.

damon_get_folio() returns NULL if the page is a tail page.  Hence I think it
will not increment sz_filter_passed multiple times?

> Hence go through the folio only once.

I tink this is still nice to do, for more efficiency.  Can you post v2 of this
patch after updating the commit message and addressing below comments?

> 
> Fixes: 6347f3385dd0 ("mm/damon/paddr: report filter-passed bytes back for DAMOS_STAT action")
> Signed-off-by: Usama Arif <usamaarif642@gmail.com>
> ---
>  mm/damon/paddr.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
> index 6b4397de4199..cc789a97c6f5 100644
> --- a/mm/damon/paddr.c
> +++ b/mm/damon/paddr.c
> @@ -504,7 +504,8 @@ static unsigned long damon_pa_stat(struct damon_region *r, struct damos *s,
>  	if (!damon_pa_scheme_has_filter(s))
>  		return 0;
>  
> -	for (addr = r->ar.start; addr < r->ar.end; addr += PAGE_SIZE) {
> +	addr = r->ar.start;
> +	while (addr < r->ar.end) {
>  		struct folio *folio = damon_get_folio(PHYS_PFN(addr));
>  
>  		if (!folio)

In this case, the code does "continue".  'addr' is not advanced, so it will
result in an infinite loop.  Let's do 'addr += PAGE_SIZE' here, to avoid that.

> @@ -515,6 +516,7 @@ static unsigned long damon_pa_stat(struct damon_region *r, struct damos *s,
>  		else
>  			*sz_filter_passed += folio_size(folio);
>  put_folio:
> +		addr += folio_size(folio);
>  		folio_put(folio);
>  	}
>  	return 0;
> -- 
> 2.43.5


Thanks,
SJ