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

On Thu, Oct 01, 2026 at 04:42:53PM +0200, Mike Rapoport wrote:

Hi Muchun,

On Tue, Sep 29, 2026 at 01:32:31PM +0800, Muchun Song wrote:

quoted

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 <redacted>
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?

IIUC, the shared tail struct pages already initialized by
vmemmap_shared_tail_page() during vmemmap population, no? It calls
set_page_node() and set_page_zone() there :)

Cheers, Lance