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Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Qi Zheng , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <20260929053231.66085-1-songmuchun@bytedance.com> <20260929053231.66085-7-songmuchun@bytedance.com> <78D5D6AA-BE36-432C-B0F7-453F93DF18C0@linux.dev> <85941AA4-7E50-4AAE-BC05-0F443B21BE8B@linux.dev> To: Mike Rapoport X-Mailer: Apple Mail (2.3901.100.1.1.12) > On Oct 6, 2026, at 12:52, Mike Rapoport wrote: >=20 > On Mon, Oct 05, 2026 at 06:27:52PM +0200, Muchun Song wrote: >>> On Oct 2, 2026, at 20:12, Mike Rapoport wrote: >>>=20 >>> On Fri, Oct 02, 2026 at 05:56:40PM +0800, Muchun Song wrote: >>>>> On Oct 2, 2026, at 16:22, Mike Rapoport wrote: >>>>=20 >>>>>>>> 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(pf= n)) && >>>>>>>> + page_zone_id(page + VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES) !=3D >>>>>>>> + page_zone_id(page)); >>>>>>>=20 >>>>>>> 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? >>>>>>=20 >>>>>> 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 =E2=80=94 right = here, after vmemmap >>>>>> population. >>>>>=20 >>>>> Still it looks out of place here, can this check be done in = sparse-vmemmap >>>>> somehow? >>>>=20 >>>> 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=E2=80=94normally 64=E2=80=94is initialized later = through >>>> __init_single_page(). >>>>=20 >>>> 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. >>>>=20 >>>> 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. >>>>=20 >>>> Would keeping the check here for now and removing it as part of >>>> that follow-up sound reasonable to you? >>>=20 >>> 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. >>>=20 >>> What do you say? >>=20 >> Sorry for the late reply because of traveling to LPC. >>=20 >> 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. >>=20 >> 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. >=20 > Yeah, putting this into all the callers sucks too :( >=20 > 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. >=20 > vmemmap_optimization_verify_zone(page, pfn) >=20 > to make it a bit nicer. Yeah, factoring this into a helper makes sense. Since it currently has only one caller, how about keeping it as a local static inline in mm_init.c instead of putting it in sparse.h? Thanks, Muchun >=20 >> Thanks, >> Muchun >>=20 >>>=20 >>>> [1] = https://lore.kernel.org/20260513132044.41690-18-songmuchun@bytedance.com/ >>>>=20 >>>> Thanks, >>>> Muchun >>>=20 >>> --=20 >>> Sincerely yours, >>> Mike. >>=20 >=20 > --=20 > Sincerely yours, > Mike.