linux-kernel - Re: [PATCH v8 1/3] mm/memory hotplug: Fix zone->contiguous always false when hotplug

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Message-ID: <c2ded9b7-c35f-4da9-bed8-b9206868a343@intel.com>
Date: Wed, 28 Jan 2026 21:49:39 +0800
From: "Li, Tianyou" <tianyou.li@...el.com>
To: Mike Rapoport <rppt@...nel.org>
CC: David Hildenbrand <david@...nel.org>, Oscar Salvador <osalvador@...e.de>,
	Wei Yang <richard.weiyang@...il.com>, Michal Hocko <mhocko@...e.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 v8 1/3] mm/memory hotplug: Fix zone->contiguous always
 false when hotplug


On 1/27/2026 2:53 PM, Mike Rapoport wrote:
> Hi,
>
> On Sat, Jan 24, 2026 at 08:18:39PM +0800, Li, Tianyou wrote:
>> On 1/22/2026 7:16 PM, Mike Rapoport wrote:
>>> On Tue, Jan 20, 2026 at 10:33:44PM +0800, Tianyou Li wrote:
>>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>>> index a63ec679d861..c8f492b5daf0 100644
>>>> --- a/mm/memory_hotplug.c
>>>> +++ b/mm/memory_hotplug.c
>>>> @@ -782,8 +782,6 @@ 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);
>>> move_pfn_range_to_zone() is also called from memremap::pagemap_range().
>>> Shouldn't we add set_zone_contiguous() there as well?
>> I did not find the place where the online_pages was invoked along path of
>> the memremap:pagemap_range() function. Would there be other functions to
>> online the pages remapped? Much appreciated for the guidance.
> Currently when we do memremap_pages() we have
>
> 	memremap_pages() ->
> 		pagemap_range() ->
> 			move_pfn_range_to_zone() ->
> 				set_zone_contiguous();
>   
> Once set_zone_contiguous() is moved out from move_pfn_range_to_zone(),
> memremap_pages() path never calls it.
> I'm not sure if the pages added in memremap_pages() are online, but to keep
> it's current behaviour I think it should call set_zone_contiguous()
> explicitly.

Thanks Mike. It's doable for me to add such a line. I am worried about 
place a set_zone_contiguous() will not add any meaningful value. Per my 
understanding, the zone contiguous will remain as false because the page 
is not online.

Regards,

Tianyou