Subject: Re: [PATCH 06/49] mm/mm_init: fix uninitialized pageblock migratetype for ZONE_DEVICE compound pages

From: Mike Rapoport <[email-masked]>
Date: Mon, 13 Apr 2026 12:32:28 +0300

On Sun, Apr 05, 2026 at 08:51:57PM +0800, Muchun Song wrote:
> Previously, memmap_init_zone_device() only initialized 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 would remain uninitialized.
> 
> This patch moves the migratetype initialization out of
> __init_zone_device_page() and into a separate function
> pageblock_migratetype_init_range(). This function 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 <[email-masked]>
> ---
>  mm/mm_init.c | 41 ++++++++++++++++++++++++++---------------
>  1 file changed, 26 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 9a44e8458fed..4936ca78966c 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -674,6 +674,18 @@ static inline void fixup_hashdist(void)
>  static inline void fixup_hashdist(void) {}
>  #endif /* CONFIG_NUMA */
>  
> +static __meminit void pageblock_migratetype_init_range(unsigned long pfn,
> +						       unsigned long nr_pages,
> +						       int migratetype)
> +{
> +	unsigned long end = pfn + nr_pages;
> +
> +	for (pfn = pageblock_align(pfn); pfn < end; pfn += pageblock_nr_pages) {
> +		init_pageblock_migratetype(pfn_to_page(pfn), migratetype, false);
> +		cond_resched();

Do we need to call cond_resched() every iteration here?

> +	}
> +}
> +
>  /*
>   * Initialize a reserved page unconditionally, finding its zone first.
>   */
> @@ -1011,21 +1023,6 @@ 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 +1119,8 @@ void __ref memmap_init_zone_device(struct zone *zone,
>  
>  		__init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
>  
> +		cond_resched();

Originally we called cond_resched() once per pageblock, now it's called
once per page plus for every pageblock in the tight loop that sets the
migrate type. Isn't it too much?

> +
>  		if (pfns_per_compound == 1)
>  			continue;
>  
> @@ -1129,6 +1128,18 @@ 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()
> +	 */
> +	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));
>  }
> -- 
> 2.20.1
> 

-- 
Sincerely yours,
Mike.