RE: [PATCH v7 2/2] mm/memory_hotplug: optimize zone contiguous check when changing pfn range

[Liu, Yuan1]

> -----Original Message-----
> From: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> Sent: Wednesday, August 26, 2026 5:06 PM
> To: Liu, Yuan1 <yuan1.liu@xxxxxxxxx>; Oscar Salvador <osalvador@xxxxxxx>;
> Mike Rapoport <rppt@xxxxxxxxxx>; Wei Yang <richard.weiyang@xxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx; Zou, Nanhai <nanhai.zou@xxxxxxxxx>; Chen Zhang
> <zhangchen.kidd@xxxxxx>; Zeng, Jason <jason.zeng@xxxxxxxxx>; Chen, Yu C
> <yu.c.chen@xxxxxxxxx>; Deng, Pan <pan.deng@xxxxxxxxx>; Li, Tianyou
> <tianyou.li@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v7 2/2] mm/memory_hotplug: optimize zone contiguous
> check when changing pfn range
> 

[...]

> It's hard to get it any cleaner. I was wondering whether we should just
> have a separate
> for_each_online_pfn() call afterwards, but that's also not ideal.
> 
> I was wondering whether we should also just use pfn_section_valid()
> directly.
> 
> Something like the following:
> 
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index e9c4204b73adb..cc7d55a71a060 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -838,22 +838,39 @@ overlap_memmap_init(unsigned long zone, unsigned
> long *pfn)
>   *   zone/node above the hole except for the trailing pages in the last
>   *   section that will be appended to the zone/node below.
>   */
> -static void __init init_unavailable_range(unsigned long spfn,
> -                                         unsigned long epfn,
> -                                         int zone, int node)
> +static unsigned long __init init_unavailable_range(unsigned long spfn,
> +                                                  unsigned long epfn,
> +                                                  int zone, int node)
>  {
> +       unsigned long next_chunk_pfn __maybe_unused = spfn;
>         unsigned long pfn;
> -       u64 pgcnt = 0;
> +       u64 online_pgcnt = 0, pgcnt = 0;
> +       bool is_online = true;
> 
>         for_each_valid_pfn(pfn, spfn, epfn) {
>                 __init_single_page(pfn_to_page(pfn), pfn, zone, node);
>                 __SetPageReserved(pfn_to_page(pfn));
>                 pgcnt++;
> +
> +               /*
> +                * With vmemmap, at this stage all pages in an early
> section
> +                * have a valid memmap and are marked as online. However,
> only
> +                * subsections in the subsection map are actually online.
> +                */
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> +               if (pfn >= next_chunk_pfn) {
> +                       is_online =
> pfn_section_valid(__pfn_to_section(pfn), pfn);
> +                       next_chunk_pfn = min(SUBSECTION_ALIGN_UP(pfn + 1),
> epfn);
> +               }
> +#endif
> +               if (is_online)
> +                       online_pgcnt++;
>         }
> 
>         if (pgcnt)
>                 pr_info("On node %d, zone %s: %lld pages in unavailable
> ranges\n",
>                         node, zone_names[zone], pgcnt);
> +       return online_pgcnt;
>  }
> 
>  /*
> 
> 
> I'd love to avoid any CONFIG_SPARSEMEM_VMEMMAP, but that's hard as well :)

Thanks, David. I'll prepare and send out the next version.

Best Regards,
Liu, Yuan

> --
> Cheers,
> 
> David