RE: [PATCH v3] mm/memory hotplug/unplug: Optimize zone contiguous check when changing pfn range

[Liu, Yuan1]

> -----Original Message-----
> From: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> Sent: Friday, April 17, 2026 5:00 PM
> To: Liu, Yuan1 <yuan1.liu@xxxxxxxxx>; Mike Rapoport <rppt@xxxxxxxxxx>
> Cc: 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 v3] mm/memory hotplug/unplug: Optimize zone contiguous
> check when changing pfn range
> 
> On 4/17/26 08:34, Liu, Yuan1 wrote:
> >
> >>>
> >>> Hi David & Mike
> >>>
> >>> I’ve spent some time working through these issues to better understand
> >> them.
> >>> For the overlapping physical spans(mirrored kernelcore), should I
> avoid
> >> counting
> >>> overlap_memmap_init in memmap_init_range in the next version?
> >>> For example, change it as follows:
> >>>
> >>> +unsigned long __meminit
> >>> +memmap_init_range(unsigned long size, int nid, unsigned long zone,
> >>> +               unsigned long start_pfn,
> >>> +               unsigned long zone_end_pfn,
> >>>                 enum meminit_context context,
> >>>                 struct vmem_altmap *altmap, int migratetype,
> >>>                 bool isolate_pageblock)
> >>>  {
> >>>         unsigned long pfn, end_pfn = start_pfn + size;
> >>> +       unsigned long nr_init = 0;
> >>>         struct page *page;
> >>>
> >>>         if (highest_memmap_pfn < end_pfn - 1)
> >>> @@ -893,7 +897,7 @@ void __meminit memmap_init_range(unsigned long
> size,
> >> int nid, unsigned long zone
> >>>         if (zone == ZONE_DEVICE) {
> >>>                 if (!altmap)
> >>> -                       return;
> >>> +                       return 0;
> >>>
> >>>                 if (start_pfn == altmap->base_pfn)
> >>>                         start_pfn += altmap->reserve;
> >>> @@ -911,6 +915,7 @@ void __meminit memmap_init_range(unsigned long
> size,
> >> int nid, unsigned long zone
> >>>                         if (defer_init(nid, pfn, zone_end_pfn)) {
> >>>                                 deferred_struct_pages = true;
> >>> +                               nr_init += end_pfn - pfn;
> >>
> >> It's confusing. Could the remaining range also include overlapping
> inits?
> >>
> >> Maybe the whole "skip overlapping init" should actually be handled on a
> >> higher level?
> >>
> >> I guess we'd want to skip any memblock_is_mirror(r) regions entirely.
> >>
> >> @Mike?
> >
> > Hi Mike
> >
> > David suggested moving the overlap handling to a higher level and
> > skipping memblock_is_mirror() regions entirely. I think this makes
> sense.
> >
> > Would this work for you, or do you have a different preference?
> 
> Would that allow for removing overlap_memmap_init() entirely? The more I
> look at that function, the more I hate it with passion :D

Yes, I think overlap_memmap_init can be removed, since we no longer need to 
check mirror PFNs in memmap_init_range and instead can check mirror regions
directly

> --
> Cheers,
> 
> David