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

Wei Yang
2020-02-05T09:59:24Z

On Sun, Oct 06, 2019 at 10:56:44AM +0200, David Hildenbrand wrote:
>If we have holes, the holes will automatically get detected and removed
>once we remove the next bigger/smaller section. The extra checks can
>go.
>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Cc: Oscar Salvador <osalvador@suse.de>
>Cc: Michal Hocko <mhocko@suse.com>
>Cc: David Hildenbrand <david@redhat.com>
>Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>Cc: Dan Williams <dan.j.williams@intel.com>
>Cc: Wei Yang <richardw.yang@linux.intel.com>
>Signed-off-by: David Hildenbrand <david@redhat.com>
>---
> mm/memory_hotplug.c | 34 +++++++---------------------------
> 1 file changed, 7 insertions(+), 27 deletions(-)
>
>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.

For example:

if () {
} else if () {
} else {
goto out;
}

/* The zone has no valid section */
if (!pfn) {
zone->zone_start_pfn = 0;
zone->spanned_pages = 0;
}

out:
zone_span_writeunlock(zone);

Well, this is just my personal taste :-)

>-
>- /*
>- * The section is not biggest or smallest mem_section in the zone, it
>- * only creates a hole in the zone. So in this case, we need not
>- * change the zone. But perhaps, the zone has only hole data. Thus
>- * it check the zone has only hole or not.
>- */
>- pfn = zone_start_pfn;
>- for (; pfn < zone_end_pfn; pfn += PAGES_PER_SUBSECTION) {
>- if (unlikely(!pfn_to_online_page(pfn)))
>- continue;
>-
>- if (page_zone(pfn_to_page(pfn)) != zone)
>- continue;
>-
>- /* Skip range to be removed */
>- if (pfn >= start_pfn && pfn < end_pfn)
>- continue;
>-
>- /* If we find valid section, we have nothing to do */
>- zone_span_writeunlock(zone);
>- return;
>- }
>-
>- /* The zone has no valid section */
>- zone->zone_start_pfn = 0;
>- zone->spanned_pages = 0;
> zone_span_writeunlock(zone);
> }
>
>--
>2.21.0

--
Wei Yang
Help you, Help me