linux-kernel - [PATCH v5 2/2] mm/memory hotplug: fix zone->contiguous always false when hotplug

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Message-ID: <20251208152544.1150732-3-tianyou.li@intel.com>
Date: Mon,  8 Dec 2025 23:25:44 +0800
From: Tianyou Li <tianyou.li@...el.com>
To: David Hildenbrand <david@...hat.com>,
	Oscar Salvador <osalvador@...e.de>,
	Mike Rapoport <rppt@...nel.org>,
	Wei Yang <richard.weiyang@...il.com>
Cc: linux-mm@...ck.org,
	Yong Hu <yong.hu@...el.com>,
	Nanhai Zou <nanhai.zou@...el.com>,
	Yuan Liu <yuan1.liu@...el.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Qiuxu Zhuo <qiuxu.zhuo@...el.com>,
	Yu C Chen <yu.c.chen@...el.com>,
	Pan Deng <pan.deng@...el.com>,
	Tianyou Li <tianyou.li@...el.com>,
	Chen Zhang <zhangchen.kidd@...com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v5 2/2] mm/memory hotplug: fix zone->contiguous always false when hotplug

From: Yuan Liu <yuan1.liu@...el.com>

Function set_zone_contiguous used __pageblock_pfn_to_page to
check the whole pageblock is in the same zone. One assumption is
the memory section must online, otherwise the __pageblock_pfn_to_page
will return NULL, then the set_zone_contiguous will be false.
When move_pfn_range_to_zone invoked set_zone_contiguous, since the
memory section did not online, the return value will always be false.

To fix this issue, we removed the set_zone_contiguous from the
move_pfn_range_to_zone, and place it after memory section onlined.

Function remove_pfn_range_from_zone did not have this issue because
memory section remains online at the time set_zone_contiguous invoked.

Reviewed-by: Tianyou Li <tianyou.li@...el.com>
Reviewed-by: Nanhai Zou <nanhai.zou@...el.com>
Signed-off-by: Yuan Liu <yuan1.liu@...el.com>
---
 mm/memory_hotplug.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index d711f6e2c87f..f548d9180415 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -809,8 +809,7 @@ void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
 {
 	struct pglist_data *pgdat = zone->zone_pgdat;
 	int nid = pgdat->node_id;
-	const enum zone_contig_state contiguous_state =
-		zone_contig_state_after_growing(zone, start_pfn, nr_pages);
+
 	clear_zone_contiguous(zone);
 
 	if (zone_is_empty(zone))
@@ -840,8 +839,6 @@ void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
 	memmap_init_range(nr_pages, nid, zone_idx(zone), start_pfn, 0,
 			 MEMINIT_HOTPLUG, altmap, migratetype,
 			 isolate_pageblock);
-
-	set_zone_contiguous(zone, contiguous_state);
 }
 
 struct auto_movable_stats {
@@ -1150,6 +1147,7 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
 {
 	unsigned long end_pfn = pfn + nr_pages;
 	int ret, i;
+	enum zone_contig_state contiguous_state = ZONE_CONTIG_NO;
 
 	ret = kasan_add_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
 	if (ret)
@@ -1164,6 +1162,10 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
 	if (mhp_off_inaccessible)
 		page_init_poison(pfn_to_page(pfn), sizeof(struct page) * nr_pages);
 
+	if (IS_ALIGNED(end_pfn, PAGES_PER_SECTION))
+		contiguous_state = zone_contig_state_after_growing(zone, pfn,
+								   nr_pages);
+
 	move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE,
 			       false);
 
@@ -1182,6 +1184,7 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
 	if (nr_pages >= PAGES_PER_SECTION)
 	        online_mem_sections(pfn, ALIGN_DOWN(end_pfn, PAGES_PER_SECTION));
 
+	set_zone_contiguous(zone, contiguous_state);
 	return ret;
 }
 
@@ -1220,6 +1223,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages,
 	};
 	const int nid = zone_to_nid(zone);
 	int need_zonelists_rebuild = 0;
+	enum zone_contig_state contiguous_state = ZONE_CONTIG_NO;
 	unsigned long flags;
 	int ret;
 
@@ -1234,6 +1238,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages,
 			 !IS_ALIGNED(pfn + nr_pages, PAGES_PER_SECTION)))
 		return -EINVAL;
 
+	contiguous_state = zone_contig_state_after_growing(zone, pfn, nr_pages);
 
 	/* associate pfn range with the zone */
 	move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_MOVABLE,
@@ -1272,6 +1277,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages,
 	}
 
 	online_pages_range(pfn, nr_pages);
+	set_zone_contiguous(zone, contiguous_state);
 	adjust_present_page_count(pfn_to_page(pfn), group, nr_pages);
 
 	if (node_arg.nid >= 0)
-- 
2.47.1