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

Baoquan He
2020-02-05T23:08:26Z

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;
}