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

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Message-ID: <0032c975-1e37-484f-9b7b-a3f0fea0401a@linux.dev>
Date: Fri, 15 Aug 2025 09:38:15 +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>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Brendan Jackman <jackmanb@...gle.com>, Johannes Weiner <hannes@...xchg.org>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: simplify lowmem_reserve max calculation



在 2025/8/14 22:47, Zi Yan 写道:
> On 14 Aug 2025, at 5:00, Ye Liu wrote:
> 
>> From: Ye Liu <liuye@...inos.cn>
>>
>> Use max() macro to simplify the calculation of maximum lowmem_reserve
>> value in calculate_totalreserve_pages(), instead of open-coding the
>> comparison. The functionality remains identical.
>>
>> Signed-off-by: Ye Liu <liuye@...inos.cn>
>> ---
>>  mm/page_alloc.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 64872214bc7d..8a55a4951d19 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -6236,8 +6236,7 @@ static void calculate_totalreserve_pages(void)
>>
>>  			/* 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];
>> +				max = max(max, zone->lowmem_reserve[j]);
>>  			}
> 
> There is a “if (max > managed_pages)” below. Maybe convert that as well?

I should use min() here, but I noticed the two variables have different types: 
one is 'long' and the other is 'unsigned long'. So, I should use min_t(). 
But then again, why is lowmem_reserve of type 'long'? 
It should be a non-negative number, right? 
Is it possible to change the type of lowmem_reserve to 'unsigned long' and 
change all uses of it at the same time? Is it necessary?

> 
> Feel free to add Acked-by: Zi Yan <ziy@...dia.com>.
> 
> Best Regards,
> Yan, Zi

-- 
Thanks,
Ye Liu