[v8] Optimize zone->contiguous update and issue fix

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

Posted by Tianyou Li 2 weeks, 5 days ago

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

set_zone_contiguous() uses __pageblock_pfn_to_page() to detect
pageblocks that either do not exist (hole) or that do not belong
to the same zone.

__pageblock_pfn_to_page(), however, relies on pfn_to_online_page(),
effectively always returning NULL for memory ranges that were not
onlined yet. So when called on a range-to-be-onlined, it indicates
a memory hole to set_zone_contiguous().

Consequently, the set_zone_contiguous() call in move_pfn_range_to_zone(),
which happens early during memory onlining, will never detect a
zone as being contiguous. Bad.

To fix the issue, move the set_zone_contiguous() call to a later
stage in memory onlining, where pfn_to_online_page() will succeed:
after we mark the memory sections to be online.

Fixes: 2d070eab2e82 ("mm: consider zone which is not fully populated to have holes")
Cc: Michal Hocko <mhocko@suse.com>
Reviewed-by: Nanhai Zou <nanhai.zou@intel.com>
Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
Signed-off-by: Tianyou Li <tianyou.li@intel.com>
---
 mm/memory_hotplug.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

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);
 }
 
 struct auto_movable_stats {
@@ -1205,6 +1203,13 @@ int online_pages(unsigned long pfn, unsigned long nr_pages,
 	}
 
 	online_pages_range(pfn, nr_pages);
+
+	/*
+	 * Now that the ranges are indicated as online, check whether the whole
+	 * zone is contiguous.
+	 */
+	set_zone_contiguous(zone);
+
 	adjust_present_page_count(pfn_to_page(pfn), group, nr_pages);
 
 	if (node_arg.nid >= 0)
-- 
2.47.1

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

Posted by Mike Rapoport 2 weeks, 3 days ago

Hi,

On Tue, Jan 20, 2026 at 10:33:44PM +0800, Tianyou Li wrote:
> From: Yuan Liu <yuan1.liu@intel.com>
> 
> set_zone_contiguous() uses __pageblock_pfn_to_page() to detect
> pageblocks that either do not exist (hole) or that do not belong
> to the same zone.
> 
> __pageblock_pfn_to_page(), however, relies on pfn_to_online_page(),
> effectively always returning NULL for memory ranges that were not
> onlined yet. So when called on a range-to-be-onlined, it indicates
> a memory hole to set_zone_contiguous().
> 
> Consequently, the set_zone_contiguous() call in move_pfn_range_to_zone(),
> which happens early during memory onlining, will never detect a
> zone as being contiguous. Bad.
> 
> To fix the issue, move the set_zone_contiguous() call to a later
> stage in memory onlining, where pfn_to_online_page() will succeed:
> after we mark the memory sections to be online.
> 
> Fixes: 2d070eab2e82 ("mm: consider zone which is not fully populated to have holes")

cc stable@ perhaps?

> Cc: Michal Hocko <mhocko@suse.com>
> Reviewed-by: Nanhai Zou <nanhai.zou@intel.com>
> Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
> Signed-off-by: Tianyou Li <tianyou.li@intel.com>
> ---
>  mm/memory_hotplug.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> 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?

>  }
>  
>  struct auto_movable_stats {
> @@ -1205,6 +1203,13 @@ int online_pages(unsigned long pfn, unsigned long nr_pages,
>  	}
>  
>  	online_pages_range(pfn, nr_pages);
> +
> +	/*
> +	 * Now that the ranges are indicated as online, check whether the whole
> +	 * zone is contiguous.
> +	 */
> +	set_zone_contiguous(zone);
> +
>  	adjust_present_page_count(pfn_to_page(pfn), group, nr_pages);
>  
>  	if (node_arg.nid >= 0)
> -- 
> 2.47.1
> 

-- 
Sincerely yours,
Mike.

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

Posted by Li, Tianyou 2 weeks, 1 day ago

Appreciated for your review, Mike.

On 1/22/2026 7:16 PM, Mike Rapoport wrote:
> Hi,
>
> On Tue, Jan 20, 2026 at 10:33:44PM +0800, Tianyou Li wrote:
>> From: Yuan Liu <yuan1.liu@intel.com>
>>
>> set_zone_contiguous() uses __pageblock_pfn_to_page() to detect
>> pageblocks that either do not exist (hole) or that do not belong
>> to the same zone.
>>
>> __pageblock_pfn_to_page(), however, relies on pfn_to_online_page(),
>> effectively always returning NULL for memory ranges that were not
>> onlined yet. So when called on a range-to-be-onlined, it indicates
>> a memory hole to set_zone_contiguous().
>>
>> Consequently, the set_zone_contiguous() call in move_pfn_range_to_zone(),
>> which happens early during memory onlining, will never detect a
>> zone as being contiguous. Bad.
>>
>> To fix the issue, move the set_zone_contiguous() call to a later
>> stage in memory onlining, where pfn_to_online_page() will succeed:
>> after we mark the memory sections to be online.
>>
>> Fixes: 2d070eab2e82 ("mm: consider zone which is not fully populated to have holes")
> cc stable@ perhaps?

Yes, will do. Thanks.

>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Reviewed-by: Nanhai Zou <nanhai.zou@intel.com>
>> Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
>> Signed-off-by: Tianyou Li <tianyou.li@intel.com>
>> ---
>>   mm/memory_hotplug.c | 9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> 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.

I leave the zone contiguous state remains the same as the optimization 
not took place in case any unexpected behavior.

>>   }
>>   
>>   struct auto_movable_stats {
>> @@ -1205,6 +1203,13 @@ int online_pages(unsigned long pfn, unsigned long nr_pages,
>>   	}
>>   
>>   	online_pages_range(pfn, nr_pages);
>> +
>> +	/*
>> +	 * Now that the ranges are indicated as online, check whether the whole
>> +	 * zone is contiguous.
>> +	 */
>> +	set_zone_contiguous(zone);
>> +
>>   	adjust_present_page_count(pfn_to_page(pfn), group, nr_pages);
>>   
>>   	if (node_arg.nid >= 0)
>> -- 
>> 2.47.1
>>

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

Posted by Mike Rapoport 1 week, 5 days ago

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.

-- 
Sincerely yours,
Mike.

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

Posted by Li, Tianyou 1 week, 4 days ago

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

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

Posted by Andrew Morton 1 week, 5 days ago

On Sat, 24 Jan 2026 20:18:39 +0800 "Li, Tianyou" <tianyou.li@intel.com> wrote:

> > cc stable@ perhaps?
> 
> Yes, will do. Thanks.

Please separate backportable patches from those which target the next
merge window.  They have different timing and take different routes
into mainline.

Thanks.

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

Posted by Li, Tianyou 1 week, 4 days ago

On 1/27/2026 5:58 AM, Andrew Morton wrote:
> On Sat, 24 Jan 2026 20:18:39 +0800 "Li, Tianyou" <tianyou.li@intel.com> wrote:
>
>>> cc stable@ perhaps?
>> Yes, will do. Thanks.
> Please separate backportable patches from those which target the next
> merge window.  They have different timing and take different routes
> into mainline.
>
> Thanks.
>
>
Appreciated Andrew for your kind explanation. My bad. Will separate it 
from the patch set in next version.

Again, thanks Mike for pointing it out.


Regards,

Tianyou