On Thu, Feb 06, 2020 at 09:50:07AM +0100, David Hildenbrand wrote:
>On 06.02.20 06:39, Baoquan He wrote:
>> In commit 950b68d9178b ("mm/memory_hotplug: don't check for "all holes"
>> in shrink_zone_span()"), the zone->zone_start_pfn/->spanned_pages
>> resetting is moved into the if()/else if() branches, if the zone becomes
>> empty. However the 2nd resetting code block may cause misunderstanding.
>>
>> So take the resetting codes out of the conditional checking and handling
>> branches just as the old code does, the find_smallest_section_pfn()and
>> find_biggest_section_pfn() searching have done the the same thing as
>> the old for loop did, the logic is kept the same as the old code. This
>> can remove the possible confusion.
>>
>> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
>> ---
>> mm/memory_hotplug.c | 14 ++++++--------
>> 1 file changed, 6 insertions(+), 8 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 089b6c826a9e..475d0d68a32c 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -398,7 +398,7 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
>> static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>> unsigned long end_pfn)
>> {
>> - unsigned long pfn;
>> + unsigned long pfn = zone->zone_start_pfn;
>> int nid = zone_to_nid(zone);
>>
>> zone_span_writelock(zone);
>> @@ -414,9 +414,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>> if (pfn) {
>> zone->spanned_pages = zone_end_pfn(zone) - pfn;
>> zone->zone_start_pfn = pfn;
>> - } else {
>> - zone->zone_start_pfn = 0;
>> - zone->spanned_pages = 0;
>> }
>> } else if (zone_end_pfn(zone) == end_pfn) {
>> /*
>> @@ -429,10 +426,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>> start_pfn);
>> if (pfn)
>> zone->spanned_pages = pfn - zone->zone_start_pfn + 1;
>> - else {
>> - zone->zone_start_pfn = 0;
>> - zone->spanned_pages = 0;
>> - }
>> + }
>> +
>> + if (!pfn) {
>> + zone->zone_start_pfn = 0;
>> + zone->spanned_pages = 0;
>> }
>> zone_span_writeunlock(zone);
>> }
>>
>
>So, what if your zone starts at pfn 0? Unlikely that we can actually
>offline that, but still it is more confusing than the old code IMHO.
>Then I prefer to drop the second else case as discussed instead.
>
Sorry, I just catch up with this thread.
If zone starts at 0, find_smallest_section_pfn() will be called only when we
want to remove the first section [0, secion_size].
Then find_smallest_section_pfn() return value has two possibilities:
* a non-0 section pfn if it still has
* 0 if the zone is empty
This looks good to me.
Or I may misunderstand your point, would you mind sharing more light on your
finding?
Thanks :-)
>--
>Thanks,
>
>David / dhildenb
--
Wei Yang
Help you, Help me
