On 02/06/20 at 09:50am, 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.
Hmm, pfn is initialized as zone->zone_start_pfn, does it matter?
The impossible empty zone won't go wrong if it really happen.
