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

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

[Ye Liu]

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

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

[Zi Yan]

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

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

[Ye Liu]

在 2025/8/15 10:36, Zi Yan 写道:
> 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);
> 
> ;)

Haha I forgot to git add after I modified it ;)

> 
>>
>>  			pgdat->totalreserve_pages += max;
>>
>> -- 
>> 2.43.0
> 
> 
> Best Regards,
> Yan, Zi

-- 
Thanks,
Ye Liu