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    Subject[PATCH v4 01/25] mm: Introduce struct folio
    Date
    A struct folio refers to an entire (possibly compound) page.  A function
    which takes a struct folio argument declares that it will operate on the
    entire compound page, not just PAGE_SIZE bytes. In return, the caller
    guarantees that the pointer it is passing does not point to a tail page.

    Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    ---
    include/linux/mm.h | 30 ++++++++++++++++++++++++++++++
    include/linux/mm_types.h | 17 +++++++++++++++++
    2 files changed, 47 insertions(+)

    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index 77e64e3eac80..a46e5a4385b0 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -927,6 +927,11 @@ static inline unsigned int compound_order(struct page *page)
    return page[1].compound_order;
    }

    +static inline unsigned int folio_order(struct folio *folio)
    +{
    + return compound_order(&folio->page);
    +}
    +
    static inline bool hpage_pincount_available(struct page *page)
    {
    /*
    @@ -1518,6 +1523,30 @@ static inline void set_page_links(struct page *page, enum zone_type zone,
    #endif
    }

    +static inline unsigned long folio_nr_pages(struct folio *folio)
    +{
    + return compound_nr(&folio->page);
    +}
    +
    +static inline struct folio *next_folio(struct folio *folio)
    +{
    +#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
    + return (struct folio *)nth_page(&folio->page, folio_nr_pages(folio));
    +#else
    + return folio + folio_nr_pages(folio);
    +#endif
    +}
    +
    +static inline unsigned int folio_shift(struct folio *folio)
    +{
    + return PAGE_SHIFT + folio_order(folio);
    +}
    +
    +static inline size_t folio_size(struct folio *folio)
    +{
    + return PAGE_SIZE << folio_order(folio);
    +}
    +
    /*
    * Some inline functions in vmstat.h depend on page_zone()
    */
    @@ -1623,6 +1652,7 @@ extern void pagefault_out_of_memory(void);

    #define offset_in_page(p) ((unsigned long)(p) & ~PAGE_MASK)
    #define offset_in_thp(page, p) ((unsigned long)(p) & (thp_size(page) - 1))
    +#define offset_in_folio(folio, p) ((unsigned long)(p) & (folio_size(folio) - 1))

    /*
    * Flags passed to show_mem() and show_free_areas() to suppress output in
    diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
    index 0974ad501a47..a311cb48526f 100644
    --- a/include/linux/mm_types.h
    +++ b/include/linux/mm_types.h
    @@ -223,6 +223,23 @@ struct page {
    #endif
    } _struct_page_alignment;

    +/*
    + * A struct folio is either a base (order-0) page or the head page of
    + * a compound page.
    + */
    +struct folio {
    + struct page page;
    +};
    +
    +static inline struct folio *page_folio(struct page *page)
    +{
    + unsigned long head = READ_ONCE(page->compound_head);
    +
    + if (unlikely(head & 1))
    + return (struct folio *)(head - 1);
    + return (struct folio *)page;
    +}
    +
    static inline atomic_t *compound_mapcount_ptr(struct page *page)
    {
    return &page[1].compound_mapcount;
    --
    2.30.0
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