linux-kernel - Re: [PATCH v2 1/2] mm/page_alloc: drop the unnecessary pfn

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Message-ID: <7525a9f6-b431-4404-2878-898e52905d4a@linux.alibaba.com>
Date:   Mon, 24 Apr 2023 18:46:40 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     akpm@...ux-foundation.org, rppt@...nel.org, ying.huang@...el.com,
        mgorman@...hsingularity.net, vbabka@...e.cz, david@...hat.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mm/page_alloc: drop the unnecessary pfn_valid()
 for start pfn



On 4/24/2023 5:50 PM, Michal Hocko wrote:
> On Sun 23-04-23 18:59:10, Baolin Wang wrote:
>> We've already used pfn_to_online_page() for start pfn to make sure
> 
> Who is we? I do not see any note explicitly requiring that start_pfn has
> to be valid for __pageblock_pfn_to_page.

Sorry for confusing, what I mean is the __pageblock_pfn_to_page() 
function, which has used pfn_to_online_page() for start pfn. So the 
pfn_valid() in __pageblock_pfn_to_page() for start pfn is unnecessary.

I will update the commit log to make it clear.

>> it is online and valid, so the pfn_valid() for the start pfn is
>> unnecessary, drop it.
>>
>> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> Reviewed-by: David Hildenbrand <david@...hat.com>
>> Reviewed-by: "Huang, Ying" <ying.huang@...el.com>
>> ---
>> Changes from v1:
>>   - Collect reviewed tags. Thanks David and Ying.
>> ---
>>   mm/page_alloc.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 9de2a18519a1..6457b64fe562 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1512,7 +1512,7 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
>>   	/* end_pfn is one past the range we are checking */
>>   	end_pfn--;
>>   
>> -	if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))
>> +	if (!pfn_valid(end_pfn))
>>   		return NULL;
>>   
>>   	start_page = pfn_to_online_page(start_pfn);
>> -- 
>> 2.27.0
>