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

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Date:   Mon, 24 Apr 2023 19:21:35 +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 6:54 PM, Michal Hocko wrote:
> On Mon 24-04-23 18:46:40, Baolin Wang wrote:
>>
>>
>> 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.
> 
> Your comment suggested that the check _has_ already been done. Which is
> not the case. pfn_to_online_page is called later in the function so I
> guess you should rephrase as following:
> 
> "
> __pageblock_pfn_to_page currently performs both pfn_valid check and
> pfn_to_online_page. The former one is redundant because the latter is a
> stronger check. Drop pfn_valid.
> "

Yes, will change the commit log.

> 
> With that or something going along with that. Feel free to add
> Acked-by: Michal Hocko <mhocko@...e.com>

Thanks.

>>>> 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
>>>
>