Re: [PATCH v3 6/6] mm/mm_init: add zone mismatch warning during page init

[Muchun Song <muchun.song@linux.dev>]

> On Oct 1, 2026, at 22:42, Mike Rapoport <rppt@kernel.org> wrote:
> 
> Hi Muchun,

Hi,

> 
> On Tue, Sep 29, 2026 at 01:32:31PM +0800, Muchun Song wrote:
>> For vmemmap-optimized sections, tail struct pages may be backed by
>> shared vmemmap pages. Those shared pages must carry the same page zone
>> ID as the struct pages initialized for the section.
>> 
>> Warn in __init_single_page() if the shared tail page has a different
>> page_zone_id(), which would indicate inconsistent initialization.
>> 
>> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>> Acked-by: Qi Zheng <qi.zheng@linux.dev>
>> ---
>> v3:
>> - Collect Acked-by from Qi Zheng
>> 
>> v2:
>> - New patch.
>> ---
>> mm/mm_init.c | 3 +++
>> 1 file changed, 3 insertions(+)
>> 
>> diff --git a/mm/mm_init.c b/mm/mm_init.c
>> index 1650d6bc1211..bd02e8d06965 100644
>> --- a/mm/mm_init.c
>> +++ b/mm/mm_init.c
>> @@ -609,6 +609,9 @@ void __meminit __init_single_page(struct page *page, unsigned long pfn,
>> if (!is_highmem_idx(zone))
>> 	set_page_address(page, __va(pfn << PAGE_SHIFT));
>> #endif
>> + 	VM_WARN_ON_ONCE(vmemmap_optimizable_order(pfn_to_section_compound_order(pfn)) &&
>> + 			page_zone_id(page + VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES) !=
>> + 			page_zone_id(page));
> 
> Hmm, page + VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES is initialized a tad later
> than page so it'll have stale data in the page->flags, won't it?

Lance is right. The shared tail struct pages are already initialized by
vmemmap_shared_tail_page() during vmemmap population, so they're not stale.
The head 64 struct pages are initialized later — right here, after vmemmap
population.

Thanks,
Muchun

> 
>> }
>> 
>> #ifdef CONFIG_NUMA
>> -- 
>> 2.54.0
>> 
> 
> -- 
> Sincerely yours,
> Mike.