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

Baoquan He
2020-02-05T23:31:10Z

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.