From 929bf010e0599ddef6b640cd314f1de65dd1ca3e Mon Sep 17 00:00:00 2001 From: Li Zhe Date: Thu, 14 Aug 2025 14:47:10 +0800 Subject: mm: introduce num_pages_contiguous() Let's add a simple helper for determining the number of contiguous pages that represent contiguous PFNs. In an ideal world, this helper would be simpler or not even required. Unfortunately, on some configs we still have to maintain (SPARSEMEM without VMEMMAP), the memmap is allocated per memory section, and we might run into weird corner cases of false positives when blindly testing for contiguous pages only. One example of such false positives would be a memory section-sized hole that does not have a memmap. The surrounding memory sections might get "struct pages" that are contiguous, but the PFNs are actually not. This helper will, for example, be useful for determining contiguous PFNs in a GUP result, to batch further operations across returned "struct page"s. VFIO will utilize this interface to accelerate the VFIO DMA map process. Implementation based on Linus' suggestions to avoid new usage of nth_page() where avoidable. Suggested-by: Linus Torvalds Suggested-by: Jason Gunthorpe Signed-off-by: Li Zhe Co-developed-by: David Hildenbrand Signed-off-by: David Hildenbrand Link: https://lore.kernel.org/r/20250814064714.56485-2-lizhe.67@bytedance.com Signed-off-by: Alex Williamson --- include/linux/mm.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'include/linux/mm.h') diff --git a/include/linux/mm.h b/include/linux/mm.h index 06978b4dbeb8..f092ce3530bb 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1833,7 +1833,12 @@ static inline unsigned long memdesc_section(memdesc_flags_t mdf) { return (mdf.f >> SECTIONS_PGSHIFT) & SECTIONS_MASK; } -#endif +#else /* !SECTION_IN_PAGE_FLAGS */ +static inline unsigned long memdesc_section(memdesc_flags_t mdf) +{ + return 0; +} +#endif /* SECTION_IN_PAGE_FLAGS */ /** * folio_pfn - Return the Page Frame Number of a folio. -- cgit v1.2.3