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

[Mike Rapoport <rppt@kernel.org>]

On Fri, Oct 02, 2026 at 09:48:42AM +0800, Muchun Song wrote:
> 
> 
> > 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.

Still it looks out of place here, can this check be done in sparse-vmemmap
somehow?
 
> Thanks,
> Muchun
> 
> > 
> >> }
> >> 
> >> #ifdef CONFIG_NUMA
> >> -- 
> >> 2.54.0
> >> 
> > 
> > -- 
> > Sincerely yours,
> > Mike.
> 
> 

-- 
Sincerely yours,
Mike.