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mm: limit folio/compound page sizes in problematic kernel configs

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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.

Link: https://lkml.kernel.org/r/20250901150359.867252-12-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2025-09-01 17:03:32 +02:00 committed by Andrew Morton
parent 99132d24d7
commit 4751c39eee
1 changed files with 18 additions and 4 deletions
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22
include/linux/mm.h
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@ -2053,11 +2053,25 @@ static inline long folio_nr_pages(const struct folio *folio)
return folio_large_nr_pages(folio);
}
/* Only hugetlbfs can allocate folios larger than MAX_ORDER */
#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
#define MAX_FOLIO_ORDER PUD_ORDER
#else
#if !defined(CONFIG_ARCH_HAS_GIGANTIC_PAGE)
/*
* We don't expect any folios that exceed buddy sizes (and consequently
* memory sections).
*/
#define MAX_FOLIO_ORDER MAX_PAGE_ORDER
#elif defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
/*
* Only pages within a single memory section are guaranteed to be
* contiguous. By limiting folios to a single memory section, all folio
* pages are guaranteed to be contiguous.
*/
#define MAX_FOLIO_ORDER PFN_SECTION_SHIFT
#else
/*
* There is no real limit on the folio size. We limit them to the maximum we
* currently expect (e.g., hugetlb, dax).
*/
#define MAX_FOLIO_ORDER PUD_ORDER
#endif
#define MAX_FOLIO_NR_PAGES (1UL << MAX_FOLIO_ORDER)