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

From: Wei Yang <[email-masked]>
Date: Wed, 5 Feb 2020 17:59:24 +0800

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 <[email-masked]>
>Cc: Oscar Salvador <[email-masked]>
>Cc: Michal Hocko <[email-masked]>
>Cc: David Hildenbrand <[email-masked]>
>Cc: Pavel Tatashin <[email-masked]>
>Cc: Dan Williams <[email-masked]>
>Cc: Wei Yang <[email-masked]>
>Signed-off-by: David Hildenbrand <[email-masked]>
>---
> 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

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