linux-kernel - Re: [PATCH v6 2/2] mm/memory hotplug: fix zone->contiguous always false when hotplug

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Message-ID: <ee63f7c4-0adc-46ec-8e14-277609af6243@intel.com>
Date: Fri, 19 Dec 2025 22:33:15 +0800
From: "Li, Tianyou" <tianyou.li@...el.com>
To: Mike Rapoport <rppt@...nel.org>
CC: David Hildenbrand <david@...hat.com>, Oscar Salvador <osalvador@...e.de>,
	Wei Yang <richard.weiyang@...il.com>, <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>, Chen Zhang <zhangchen.kidd@...com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 2/2] mm/memory hotplug: fix zone->contiguous always
 false when hotplug


On 12/19/2025 5:37 PM, Mike Rapoport wrote:
> Hi,
>
> On Mon, Dec 15, 2025 at 09:04:37PM +0800, Tianyou Li wrote:
>> 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.
> Since the fix is relevant even without the optimization patch, can we
> please reorder the patches so that the fix will be the first in the series?
> Than it can be applied to stable trees as well.


Thanks for the comments. That's totally make sense. I will work on the 
patch v7, will rebase with 6.19-rc1. I will be out of office next week, 
probably slow response but will keep working on the patch with Yuan Liu. 
Thanks.


Regards,

Tianyou


>   
>> 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 | 18 ++++++++++++++----
>>   1 file changed, 14 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 12839032ad42..0220021f6a68 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -810,8 +810,7 @@ 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 new_contiguous_state =
>> -		zone_contig_state_after_growing(zone, start_pfn, nr_pages);
>> +
>>   	clear_zone_contiguous(zone);
>>   
>>   	if (zone_is_empty(zone))
>> @@ -841,8 +840,6 @@ 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, new_contiguous_state);
>>   }
>>   
>>   struct auto_movable_stats {
>> @@ -1151,6 +1148,7 @@ 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 new_contiguous_state = ZONE_CONTIG_NO;
>>   
>>   	ret = kasan_add_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
>>   	if (ret)
>> @@ -1165,6 +1163,14 @@ 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 the allocated memmap pages are not in a full section, keep the
>> +	 * contiguous state as ZONE_CONTIG_NO.
>> +	 */
>> +	if (IS_ALIGNED(end_pfn, PAGES_PER_SECTION))
>> +		new_contiguous_state = zone_contig_state_after_growing(zone,
>> +								pfn, nr_pages);
>> +
>>   	move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE,
>>   			       false);
>>   
>> @@ -1183,6 +1189,7 @@ 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, new_contiguous_state);
>>   	return ret;
>>   }
>>   
>> @@ -1221,6 +1228,7 @@ 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 new_contiguous_state = ZONE_CONTIG_NO;
>>   	unsigned long flags;
>>   	int ret;
>>   
>> @@ -1235,6 +1243,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages,
>>   			 !IS_ALIGNED(pfn + nr_pages, PAGES_PER_SECTION)))
>>   		return -EINVAL;
>>   
>> +	new_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,
>> @@ -1273,6 +1282,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages,
>>   	}
>>   
>>   	online_pages_range(pfn, nr_pages);
>> +	set_zone_contiguous(zone, new_contiguous_state);
>>   	adjust_present_page_count(pfn_to_page(pfn), group, nr_pages);
>>   
>>   	if (node_arg.nid >= 0)
>> -- 
>> 2.47.1
>>