Re: [PATCH v2 6/6] mm/mm_init: Fix pageblock migratetype for ZONE_DEVICE compound pages

[Muchun Song]

> On Apr 16, 2026, at 01:03, Mike Rapoport <rppt@xxxxxxxxxx> wrote:
> 
> Hi Muchun,
> 
> On Wed, Apr 15, 2026 at 07:14:12PM +0800, 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@xxxxxxxxxxxxx>
>> ---
>> mm/mm_init.c | 42 +++++++++++++++++++++++++++---------------
>> 1 file changed, 27 insertions(+), 15 deletions(-)
>> 
>> diff --git a/mm/mm_init.c b/mm/mm_init.c
>> index f9f8e1af921c..30528c4206c1 100644
>> --- a/mm/mm_init.c
>> +++ b/mm/mm_init.c
>> @@ -674,6 +674,19 @@ 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);
>> + 		if (IS_ALIGNED(pfn, PAGES_PER_SECTION))
>> + 			cond_resched();
>> + 	}
>> +}
>> +
>> /*
>>  * Initialize a reserved page unconditionally, finding its zone first.
>>  */
>> @@ -1011,21 +1024,6 @@ 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 +1120,8 @@ void __ref memmap_init_zone_device(struct zone *zone,
>> 
>> 	__init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
>> 
>> + 	cond_resched();
>> +
> 
> I don't think we want cond_resched() for every page here too, even it's a
> compound page :)

I'll update it to every PAGES_PER_SECTION, does this make sense for you?

Thanks,
Muchun

> 
> Otherwise
> 
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
> 
>> if (pfns_per_compound == 1)
>> continue;
>> 
>> @@ -1129,6 +1129,18 @@ 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.