linux-kernel - Re: [PATCH 1/3] mm/mm_init.c: remove comments in zone_spanned_pages_in_node() and zone_absent_pages_in

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Message-ID: <5453d94d-c231-6d50-02bd-a510109bb306@shopee.com>
Date:   Thu, 25 May 2023 22:07:39 +0800
From:   Haifeng Xu <haifeng.xu@...pee.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     akpm@...ux-foundation.org, mhocko@...e.com, david@...hat.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] mm/mm_init.c: remove comments in
 zone_spanned_pages_in_node() and zone_absent_pages_in_node()



On 2023/5/25 16:24, Mike Rapoport wrote:
> On Thu, May 25, 2023 at 04:01:48AM +0000, Haifeng Xu wrote:
>> Since commit 03e85f9d5f1f ("mm/page_alloc: Introduce free_area_init_core_hotplug"),
>> free_area_init_node() doesn't get called in hotplug path anymore, so
>> remove the comments related to it.
>>
>> Signed-off-by: Haifeng Xu <haifeng.xu@...pee.com>
>> ---
>>  mm/mm_init.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/mm/mm_init.c b/mm/mm_init.c
>> index 7f7f9c677854..cf55bba04b23 100644
>> --- a/mm/mm_init.c
>> +++ b/mm/mm_init.c
>> @@ -1174,7 +1174,6 @@ static unsigned long __init zone_absent_pages_in_node(int nid,
>>  	unsigned long zone_start_pfn, zone_end_pfn;
>>  	unsigned long nr_absent;
>>  
>> -	/* When hotadd a new node from cpu_up(), the node should be empty */
>>  	if (!node_start_pfn && !node_end_pfn)
>>  		return 0;
> 
> I think it's better to call calculate_node_totalpages only if node actually has 
> memory and for node with no memory we just need to make sure all the node
> and zone page counts are indeed set to 0.

Yes, it's good advice.

> 
> Then the condition here and in zone_spanned_pages_in_node() can be removed
> along with the comment and patch 2 won't be required at all.

Regarding to patch 2, if the node has mmeory but contains zone with no memory,
it can avoid the calculation of absent pages.

I thik we can add a check that whether zone_end_pfn is equal to zone_start_pfn
in patch 3. If it's true, return 0 directly. So patch 2 can be dropped.

Thanks!

>   
>> @@ -1227,7 +1226,7 @@ static unsigned long __init zone_spanned_pages_in_node(int nid,
>>  {
>>  	unsigned long zone_low = arch_zone_lowest_possible_pfn[zone_type];
>>  	unsigned long zone_high = arch_zone_highest_possible_pfn[zone_type];
>> -	/* When hotadd a new node from cpu_up(), the node should be empty */
>> +
>>  	if (!node_start_pfn && !node_end_pfn)
>>  		return 0;
>>  
>> -- 
>> 2.25.1
>>
>>
>