Re: [PATCH v2] mm/page_alloc: simplify lowmem_reserve max calculation

[Zi Yan <ziy@nvidia.com>]

On 14 Aug 2025, at 22:34, Ye Liu wrote:

> From: Ye Liu <liuye@kylinos.cn>
>
> Use max() to find the maximum lowmem_reserve value and min_t() to
> cap it to managed_pages in calculate_totalreserve_pages(), instead
> of open-coding the comparisons. No functional change.
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Acked-by: Zi Yan <ziy@nvidia.com>
>
> Changes in v2:
> - Drop unnecessary braces
> - Replace "if (max > managed_pages)" with min_t()
> - Link to v1:https://lore.kernel.org/all/20250814090053.22241-1-ye.liu@linux.dev/
> ---
>  mm/page_alloc.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 64872214bc7d..2617fd2f4b73 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6235,16 +6235,13 @@ static void calculate_totalreserve_pages(void)
>  			unsigned long managed_pages = zone_managed_pages(zone);
>
>  			/* Find valid and maximum lowmem_reserve in the zone */
> -			for (j = i; j < MAX_NR_ZONES; j++) {
> -				if (zone->lowmem_reserve[j] > max)
> -					max = zone->lowmem_reserve[j];
> -			}
> +			for (j = i; j < MAX_NR_ZONES; j++)
> +				max = max(max, zone->lowmem_reserve[j]);
>
>  			/* we treat the high watermark as reserved pages. */
>  			max += high_wmark_pages(zone);
>
> -			if (max > managed_pages)
> -				max = managed_pages;
> +			min_t(unsigned long, max, managed_pages);

Should be

max = min_t(unsigned long, max, managed_pages);

;)

>
>  			pgdat->totalreserve_pages += max;
>
> -- 
> 2.43.0


Best Regards,
Yan, Zi