Re: [PATCH v4 4/5] mm/mm_init: Fix pageblock migratetype for ZONE_DEVICE compound pages

David Hildenbrand (Arm)
2026-04-22T19:03:30Z

On 4/22/26 10:14, Muchun Song wrote:
> The memmap_init_zone_device() function only initializes the migratetype
> of the first pageblock of a compound page. If the compound page size
> exceeds pageblock_nr_pages (e.g., 1GB hugepages with 2MB pageblocks),
> subsequent pageblocks in the compound page remain uninitialized.
>
> Move the migratetype initialization out of __init_zone_device_page()
> and into a separate pageblock_migratetype_init_range() function. This
> iterates over the entire PFN range of the memory, ensuring that all
> pageblocks are correctly initialized.
>
> Fixes: c4386bd8ee3a ("mm/memremap: add ZONE_DEVICE support for compound pages")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> ---
> mm/mm_init.c | 45 ++++++++++++++++++++++++++++++---------------
> 1 file changed, 30 insertions(+), 15 deletions(-)
>
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index f9f8e1af921c..9d0fe79a94de 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -674,6 +674,21 @@ static inline void fixup_hashdist(void)
> static inline void fixup_hashdist(void) {}
> #endif /* CONFIG_NUMA */
>
> +#ifdef CONFIG_ZONE_DEVICE
> +static __meminit void pageblock_migratetype_init_range(unsigned long pfn,
> + unsigned long nr_pages,
> + int migratetype)

Two-tab indent says hi :)

> +{
> + unsigned long end = pfn + nr_pages;

Can be const.

> +
> + for (pfn = pageblock_align(pfn); pfn < end; pfn += pageblock_nr_pages) {
> + init_pageblock_migratetype(pfn_to_page(pfn), migratetype, false);
> + if (IS_ALIGNED(pfn, PAGES_PER_SECTION))
> + cond_resched();
> + }
> +}
> +#endif
> +
> /*
> * Initialize a reserved page unconditionally, finding its zone first.
> */
> @@ -1011,21 +1026,6 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
> page_folio(page)->pgmap = pgmap;
> page->zone_device_data = NULL;
>
> - /*
> - * Mark the block movable so that blocks are reserved for
> - * movable at startup. This will force kernel allocations
> - * to reserve their blocks rather than leaking throughout
> - * the address space during boot when many long-lived
> - * kernel allocations are made.
> - *
> - * Please note that MEMINIT_HOTPLUG path doesn't clear memmap
> - * because this is done early in section_activate()
> - */
> - if (pageblock_aligned(pfn)) {
> - init_pageblock_migratetype(page, MIGRATE_MOVABLE, false);
> - cond_resched();
> - }
> -
> /*
> * ZONE_DEVICE pages other than MEMORY_TYPE_GENERIC are released
> * directly to the driver page allocator which will set the page count
> @@ -1122,6 +1122,9 @@ void __ref memmap_init_zone_device(struct zone *zone,
>
> __init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
>
> + if (IS_ALIGNED(pfn, PAGES_PER_SECTION))
> + cond_resched();
> +
> if (pfns_per_compound == 1)
> continue;
>
> @@ -1129,6 +1132,18 @@ void __ref memmap_init_zone_device(struct zone *zone,
> compound_nr_pages(altmap, pgmap));
> }
>
> + /*
> + * Mark the block movable so that blocks are reserved for
> + * movable at startup. This will force kernel allocations
> + * to reserve their blocks rather than leaking throughout
> + * the address space during boot when many long-lived
> + * kernel allocations are made.
> + *
> + * Please note that MEMINIT_HOTPLUG path doesn't clear memmap
> + * because this is done early in section_activate()
> + */

I am deeply confused about the "memmap" comment here.

There is no MEMINIT_HOTPLUG special-casing. Nobody "clears memmap".

That comment was introduced in

commit 966cf44f637e6aeea7e3d01ba004bf8b5beac78f
Author: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Date: Fri Oct 26 15:07:52 2018 -0700

mm: defer ZONE_DEVICE page initialization to the point where we init pgmap

Where we added memmap_init_zone_device().

Is that commit still valid, and this it actually belong here, above the
migratetype setting?

> + pageblock_migratetype_init_range(start_pfn, nr_pages, MIGRATE_MOVABLE);
> +
> pr_debug("%s initialised %lu pages in %ums\n", __func__,
> nr_pages, jiffies_to_msecs(jiffies - start));
> }

--
Cheers,

David