netdev - Re: [PATCH v1 12/36] mm: simplify folio_page() and folio_page

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Message-ID: <oinnsfpimax75klq74eb3orjaoipl6szcjlfhfes6gvnmyvb4m@xdpb7l3igqt3>
Date: Fri, 29 Aug 2025 10:41:16 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, Zi Yan <ziy@...dia.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
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        Christoph Lameter <cl@...two.org>, Dennis Zhou <dennis@...nel.org>,
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        intel-gfx@...ts.freedesktop.org, iommu@...ts.linux.dev,
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Subject: Re: [PATCH v1 12/36] mm: simplify folio_page() and folio_page_idx()

* David Hildenbrand <david@...hat.com> [250827 18:06]:
> Now that a single folio/compound page can no longer span memory sections
> in problematic kernel configurations, we can stop using nth_page().

..but only in a subset of nth_page uses, considering mm.h still has the
define.


> 
> While at it, turn both macros into static inline functions and add
> kernel doc for folio_page_idx().
> 
> Reviewed-by: Zi Yan <ziy@...dia.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>

> ---
>  include/linux/mm.h         | 16 ++++++++++++++--
>  include/linux/page-flags.h |  5 ++++-
>  2 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 2dee79fa2efcf..f6880e3225c5c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -210,10 +210,8 @@ extern unsigned long sysctl_admin_reserve_kbytes;
>  
>  #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
>  #define nth_page(page,n) pfn_to_page(page_to_pfn((page)) + (n))
> -#define folio_page_idx(folio, p)	(page_to_pfn(p) - folio_pfn(folio))
>  #else
>  #define nth_page(page,n) ((page) + (n))
> -#define folio_page_idx(folio, p)	((p) - &(folio)->page)
>  #endif
>  
>  /* to align the pointer to the (next) page boundary */
> @@ -225,6 +223,20 @@ extern unsigned long sysctl_admin_reserve_kbytes;
>  /* test whether an address (unsigned long or pointer) is aligned to PAGE_SIZE */
>  #define PAGE_ALIGNED(addr)	IS_ALIGNED((unsigned long)(addr), PAGE_SIZE)
>  
> +/**
> + * folio_page_idx - Return the number of a page in a folio.
> + * @folio: The folio.
> + * @page: The folio page.
> + *
> + * This function expects that the page is actually part of the folio.
> + * The returned number is relative to the start of the folio.
> + */
> +static inline unsigned long folio_page_idx(const struct folio *folio,
> +		const struct page *page)
> +{
> +	return page - &folio->page;
> +}
> +
>  static inline struct folio *lru_to_folio(struct list_head *head)
>  {
>  	return list_entry((head)->prev, struct folio, lru);
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 5ee6ffbdbf831..faf17ca211b4f 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -316,7 +316,10 @@ static __always_inline unsigned long _compound_head(const struct page *page)
>   * check that the page number lies within @folio; the caller is presumed
>   * to have a reference to the page.
>   */
> -#define folio_page(folio, n)	nth_page(&(folio)->page, n)
> +static inline struct page *folio_page(struct folio *folio, unsigned long n)
> +{
> +	return &folio->page + n;
> +}
>  
>  static __always_inline int PageTail(const struct page *page)
>  {
> -- 
> 2.50.1
> 
>