On Mon, Oct 05, 2026 at 06:27:52PM +0200, Muchun Song wrote: > > On Oct 2, 2026, at 20:12, Mike Rapoport <[email protected]> wrote: > > > > On Fri, Oct 02, 2026 at 05:56:40PM +0800, Muchun Song wrote: > >>> On Oct 2, 2026, at 16:22, Mike Rapoport <[email protected]> wrote: > >> > >>>>>> 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? > >> > >> The struct page entries of a vmemmap-optimizable compound page > >> are currently initialized in two stages. During vmemmap > >> population, the shared tail entries are initialized first. The > >> retained head area—normally 64—is initialized later through > >> __init_single_page(). > >> > >> This warning connects the two stages: while initializing the > >> retained entries in the second stage, it verifies that their zone > >> information is consistent with the shared entries initialized in > >> the first stage. Therefore, the same check cannot be performed > >> during vmemmap population. > >> > >> I am planning to first unify the HugeTLB and Device DAX > >> compound-page initialization through a common helper [1]. Once that > >> work is complete, maybe it will be easy to move the initialization > >> of the retained head area into vmemmap population. With both the > >> retained and shared entries initialized in the same stage, there > >> will be no cross-stage inconsistency to check, and this warning > >> can be removed. > >> > >> Would keeping the check here for now and removing it as part of > >> that follow-up sound reasonable to you? > > > > While it feels really out of place in __init_single_page(), but having it > > memmap_init_range() close to the if that skips shared tail pages makes > > sense. > > > > What do you say? > > Sorry for the late reply because of traveling to LPC. > > Putting the check in memmap_init_range() would validate the > invariant for the shared-tail range skipped there. It would > not, however, cover all vmemmap-optimized initialization > paths: optimized Device DAX bypasses memmap_init_range() > when there is no altmap, and deferred boot-time HugeTLB > initialization may also initialize retained entries > elsewhere. > > If the intention is to validate only the skip in > memmap_init_range(), moving it there makes sense. If we want > the warning to cover both HugeTLB and Device DAX generally, > it still needs to remain in __init_single_page() or be > called from the individual initialization paths.
Yeah, putting this into all the callers sucks too :( With all the callers,__init_single_page() is the right place for this check, but I think we can add a static inline in sparse.h, like e.g. vmemmap_optimization_verify_zone(page, pfn) to make it a bit nicer. > Thanks, > Muchun > > > > >> [1] > >> https://lore.kernel.org/[email protected]/ > >> > >> Thanks, > >> Muchun > > > > -- > > Sincerely yours, > > Mike. > -- Sincerely yours, Mike.
