linux-kernel - [PATCH] mm/hotplug: Adjust shrink_zone

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Date:   Thu,  6 Feb 2020 13:39:12 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        richardw.yang@...ux.intel.com, david@...hat.com, mhocko@...e.com,
        osalvador@...e.de, bhe@...hat.com
Subject: [PATCH] mm/hotplug: Adjust shrink_zone_span() to keep the old logic

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@...hat.com>
---
 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);
 }
-- 
2.17.2