linux-kernel - Re: [PATCH v2] mm/page_alloc: simplify lowmem

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Message-ID: <E5434A0E-3125-48C7-BD25-185CDA4D9FAC@nvidia.com>
Date: Thu, 14 Aug 2025 22:36:59 -0400
From: Zi Yan <ziy@...dia.com>
To: Ye Liu <ye.liu@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Vlastimil Babka <vbabka@...e.cz>, Ye Liu <liuye@...inos.cn>,
 Johannes Weiner <hannes@...xchg.org>, Suren Baghdasaryan <surenb@...gle.com>,
 Michal Hocko <mhocko@...e.com>, Brendan Jackman <jackmanb@...gle.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/page_alloc: simplify lowmem_reserve max calculation

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

> From: Ye Liu <liuye@...inos.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@...inos.cn>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
> Acked-by: Zi Yan <ziy@...dia.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