[PATCH v1 11/36] mm: limit folio/compound page sizes in problematic kernel configs

[Wei Yang]

On Thu, Aug 28, 2025 at 12:01:15AM +0200, David Hildenbrand wrote:
>Let's limit the maximum folio size in problematic kernel config where
>the memmap is allocated per memory section (SPARSEMEM without
>SPARSEMEM_VMEMMAP) to a single memory section.
>
>Currently, only a single architectures supports ARCH_HAS_GIGANTIC_PAGE
>but not SPARSEMEM_VMEMMAP: sh.
>
>Fortunately, the biggest hugetlb size sh supports is 64 MiB
>(HUGETLB_PAGE_SIZE_64MB) and the section size is at least 64 MiB
>(SECTION_SIZE_BITS == 26), so their use case is not degraded.
>
>As folios and memory sections are naturally aligned to their order-2 size
>in memory, consequently a single folio can no longer span multiple memory
>sections on these problematic kernel configs.
>
>nth_page() is no longer required when operating within a single compound
>page / folio.
>
>Reviewed-by: Zi Yan <ziy at nvidia.com>
>Acked-by: Mike Rapoport (Microsoft) <rppt at kernel.org>
>Signed-off-by: David Hildenbrand <david at redhat.com>

Reviewed-by: Wei Yang <richard.weiyang at gmail.com>

-- 
Wei Yang
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