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

[Liu, Yuan1]

> -----Original Message-----
> From: Mike Rapoport <rppt@xxxxxxxxxx>
> Sent: Monday, April 20, 2026 10:03 PM
> To: Liu, Yuan1 <yuan1.liu@xxxxxxxxx>
> Cc: David Hildenbrand (Arm) <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 v3] mm/memory hotplug/unplug: Optimize zone contiguous
> check when changing pfn range
> 
> On Fri, Apr 17, 2026 at 06:34:50AM +0000, Liu, Yuan1 wrote:
> >
> > > >>> sashiko had several comments
> > > >>> https://sashiko.dev/#/patchset/20260408031615.1831922-1-
> > > >> yuan1.liu%40intel.com
> > > >>>
> > > >>> I skipped the ones related to hotplug, but in the mm_init part the
> > > >> comment
> > > >>> about zones that can have overlapping physical spans when mirrored
> > > >>> kernelcore is enabled seems valid.
> > > >
> > > > 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?
> 
> Looks about right :)

Thanks for the review. I’ll keep working on the patch.

> > Something like this
> > static void __init memmap_init(void)
> > {
> > ...
> >     for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid)
> {
> >         struct pglist_data *node = NODE_DATA(nid);
> >         bool is_mirror = mirrored_kernelcore &&
> > 				 memblock_is_mirror(&memblock.memory.regions[i]);
> 
> I'd add a local memblock_region variable.

I’ll refine this in the next version.

> >
> >         for (j = 0; j < MAX_NR_ZONES; j++) {
> >         ...
> > 	      if (is_mirror && j == ZONE_MOVABLE)
> >                 continue;
> >
> >            memmap_init_zone_range(zone, start_pfn, end_pfn,
> >                                   &hole_pfn);
> > Best Regards,
> > Liu, Yuan1
> 
> --
> Sincerely yours,
> Mike.