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

Wei Yang
2020-02-05T23:34:28Z

On Thu, Feb 06, 2020 at 07:30:51AM +0800, Baoquan He wrote:
>On 02/06/20 at 07:26am, Wei Yang wrote:
>> 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 for your confirmation, I will make one patch like this and post.

Sure :-)

--
Wei Yang
Help you, Help me