From: Mike Rapoport <rppt@xxxxxxxxxxxxx> Subject: include/linux/mmzone.h: add documentation for pfn_valid() Patch series "arm64: drop pfn_valid_within() and simplify pfn_valid()", v4. These patches aim to remove CONFIG_HOLES_IN_ZONE and essentially hardwire pfn_valid_within() to 1. The idea is to mark NOMAP pages as reserved in the memory map and restore the intended semantics of pfn_valid() to designate availability of struct page for a pfn. With this the core mm will be able to cope with the fact that it cannot use NOMAP pages and the holes created by NOMAP ranges within MAX_ORDER blocks will be treated correctly even without the need for pfn_valid_within. This patch (of 4): Add comment describing the semantics of pfn_valid() that clarifies that pfn_valid() only checks for availability of a memory map entry (i.e. struct page) for a PFN rather than availability of usable memory backing that PFN. The most "generic" version of pfn_valid() used by the configurations with SPARSEMEM enabled resides in include/linux/mmzone.h so this is the most suitable place for documentation about semantics of pfn_valid(). Link: https://lkml.kernel.org/r/20210511100550.28178-1-rppt@xxxxxxxxxx Link: https://lkml.kernel.org/r/20210511100550.28178-2-rppt@xxxxxxxxxx Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> Suggested-by: Anshuman Khandual <anshuman.khandual@xxxxxxx> Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx> Acked-by: Ard Biesheuvel <ardb@xxxxxxxxxx> Reviewed-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Marc Zyngier <maz@xxxxxxxxxx> Cc: Mark Rutland <mark.rutland@xxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/mmzone.h | 11 +++++++++++ 1 file changed, 11 insertions(+) --- a/include/linux/mmzone.h~include-linux-mmzoneh-add-documentation-for-pfn_valid +++ a/include/linux/mmzone.h @@ -1445,6 +1445,17 @@ static inline int pfn_section_valid(stru #endif #ifndef CONFIG_HAVE_ARCH_PFN_VALID +/** + * pfn_valid - check if there is a valid memory map entry for a PFN + * @pfn: the page frame number to check + * + * Check if there is a valid memory map entry aka struct page for the @pfn. + * Note, that availability of the memory map entry does not imply that + * there is actual usable memory at that @pfn. The struct page may + * represent a hole or an unusable page frame. + * + * Return: 1 for PFNs that have memory map entries and 0 otherwise + */ static inline int pfn_valid(unsigned long pfn) { struct mem_section *ms; _
