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

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Message-ID: <be1a8882-fb43-4038-a500-01c3e1a6d577@linux.dev>
Date: Fri, 15 Aug 2025 10:41:16 +0800
From: Ye Liu <ye.liu@...ux.dev>
To: Zi Yan <ziy@...dia.com>
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



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

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

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

-- 
Thanks,
Ye Liu