Subject: Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

From: David Hildenbrand <[email-masked]>
Date: Tue, 4 Feb 2020 15:42:56 +0100

On 04.02.20 15:25, Baoquan He wrote:
> On 10/06/19 at 10:56am, David Hildenbrand wrote:
>> If we have holes, the holes will automatically get detected and removed
>> once we remove the next bigger/smaller section. The extra checks can
>> go.
>>
>> Cc: Andrew Morton <[email-masked]>
>> Cc: Oscar Salvador <[email-masked]>
>> Cc: Michal Hocko <[email-masked]>
>> Cc: David Hildenbrand <[email-masked]>
>> Cc: Pavel Tatashin <[email-masked]>
>> Cc: Dan Williams <[email-masked]>
>> Cc: Wei Yang <[email-masked]>
>> Signed-off-by: David Hildenbrand <[email-masked]>
>> ---
>>  mm/memory_hotplug.c | 34 +++++++---------------------------
>>  1 file changed, 7 insertions(+), 27 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index f294918f7211..8dafa1ba8d9f 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>>  		if (pfn) {
>>  			zone->zone_start_pfn = pfn;
>>  			zone->spanned_pages = zone_end_pfn - pfn;
>> +		} else {
>> +			zone->zone_start_pfn = 0;
>> +			zone->spanned_pages = 0;
>>  		}
>>  	} else if (zone_end_pfn == end_pfn) {
>>  		/*
>> @@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>>  					       start_pfn);
>>  		if (pfn)
>>  			zone->spanned_pages = pfn - zone_start_pfn + 1;
>> +		else {
>> +			zone->zone_start_pfn = 0;
>> +			zone->spanned_pages = 0;
> 
> Thinking in which case (zone_start_pfn != start_pfn) and it comes here.

Could only happen in case the zone_start_pfn would have been "out of the
zone already". If you ask me: unlikely :)

This change at least maintains the same result as before (where the
all-holes check would have caught it).

-- 
Thanks,

David / dhildenb

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