RE: [PATCH] mm/memory hotplug/unplug: Optimize zone contiguous check when changing pfn range

[Liu, Yuan1]

> -----Original Message-----
> From: Mike Rapoport <rppt@xxxxxxxxxx>
> Sent: Monday, March 23, 2026 7:51 PM
> To: Liu, Yuan1 <yuan1.liu@xxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>; Oscar Salvador
> <osalvador@xxxxxxx>; Wei Yang <richard.weiyang@xxxxxxxxx>; linux-
> mm@xxxxxxxxx; Hu, Yong <yong.hu@xxxxxxxxx>; Zou, Nanhai
> <nanhai.zou@xxxxxxxxx>; Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>; Zhuo, Qiuxu
> <qiuxu.zhuo@xxxxxxxxx>; Chen, Yu C <yu.c.chen@xxxxxxxxx>; Deng, Pan
> <pan.deng@xxxxxxxxx>; Li, Tianyou <tianyou.li@xxxxxxxxx>; Chen Zhang
> <zhangchen.kidd@xxxxxx>; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH] mm/memory hotplug/unplug: Optimize zone contiguous
> check when changing pfn range
> 
> Hi,
> 
> On Thu, Mar 19, 2026 at 05:56:22AM -0400, Yuan Liu wrote:
> 
> ...
> 
> > diff --git a/mm/mm_init.c b/mm/mm_init.c
> > index df34797691bd..96690e550024 100644
> > --- a/mm/mm_init.c
> > +++ b/mm/mm_init.c
> > @@ -946,6 +946,7 @@ static void __init memmap_init_zone_range(struct
> zone *zone,
> >  	unsigned long zone_start_pfn = zone->zone_start_pfn;
> >  	unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages;
> >  	int nid = zone_to_nid(zone), zone_id = zone_idx(zone);
> > +	unsigned long zone_hole_start, zone_hole_end;
> >
> >  	start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn);
> >  	end_pfn = clamp(end_pfn, zone_start_pfn, zone_end_pfn);
> > @@ -957,8 +958,19 @@ static void __init memmap_init_zone_range(struct
> zone *zone,
> >  			  zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE,
> >  			  false);
> >
> > -	if (*hole_pfn < start_pfn)
> > +	WRITE_ONCE(zone->pages_with_online_memmap,
> > +		   READ_ONCE(zone->pages_with_online_memmap) +
> > +		   (end_pfn - start_pfn));
> > +
> > +	if (*hole_pfn < start_pfn) {
> >  		init_unavailable_range(*hole_pfn, start_pfn, zone_id, nid);
> > +		zone_hole_start = clamp(*hole_pfn, zone_start_pfn,
> zone_end_pfn);
> > +		zone_hole_end = clamp(start_pfn, zone_start_pfn,
> zone_end_pfn);
> > +		if (zone_hole_start < zone_hole_end)
> > +			WRITE_ONCE(zone->pages_with_online_memmap,
> > +				   READ_ONCE(zone->pages_with_online_memmap) +
> > +				   (zone_hole_end - zone_hole_start));
> > +	}
> 
> I didn't have time to review it, but it really jumped at me.
> memmap_init_zone_range() runs before SMP, there is no need for
> WRITE_ONCE()/READ_ONCE() here.

Hi Mike

Thank you very much for taking the time to review this patch. I will fix it.

> --
> Sincerely yours,
> Mike.