Re: [PATCH v4 1/4] include/linux/mmzone.h: add documentation for pfn_valid()

[Ard Biesheuvel]

On Tue, 11 May 2021 at 12:06, Mike Rapoport <rppt@xxxxxxxxxx> wrote:
>
> From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
>
> 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().
>
> Suggested-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>

Acked-by: Ard Biesheuvel <ardb@xxxxxxxxxx>

> ---
>  include/linux/mmzone.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 0d53eba1c383..e5945ca24df7 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1427,6 +1427,17 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
>  #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;
> --
> 2.28.0
>