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

Wei Yang
2020-02-05T23:26:20Z

On Thu, Feb 06, 2020 at 07:08:26AM +0800, Baoquan He wrote:
>On 02/06/20 at 06:56am, Wei Yang wrote:
>> On Wed, Feb 05, 2020 at 10:48:11PM +0800, Baoquan He wrote:
>> >Hi Wei Yang,
>> >
>> >On 02/05/20 at 05:59pm, Wei Yang wrote:
>> >> >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;
>> >> >+ }
>> >> > }
>> >>
>> >> If it is me, I would like to take out these two similar logic out.
>> >
>> >I also like this style.
>> >>
>> >> For example:
>> >>
>> >> if () {
>> >> } else if () {
>> >> } else {
>> >> goto out;
>> >Here the last else is unnecessary, right?
>> >
>>
>> I am afraid not.
>>
>> If the range is not the first or last, we would leave pfn not initialized.
>
>Ah, you are right. I forgot that one. Then pfn can be assigned the
>zone_start_pfn as the old code. Then the following logic is the same
>as the original code, find_smallest_section_pfn()/find_biggest_section_pfn()
>have done the iteration the old for loop was doing.
>
> unsigned long pfn = zone_start_pfn;
> if () {
> } else if () {
> }
>
> /* The zone has no valid section */
> if (!pfn) {
> zone->zone_start_pfn = 0;
> zone->spanned_pages = 0;
> }

This one look better :-)

Thanks

--
Wei Yang
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