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

[Mike Rapoport <rppt@kernel.org>]

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 :)
 
> 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.

> 
>         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.