Messages in this thread Patch in this message | | | Date | Sat, 13 Mar 2021 12:37:02 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH v4 01/25] mm: Introduce struct folio |
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On Fri, 5 Mar 2021 04:18:37 +0000 "Matthew Wilcox (Oracle)" <willy@infradead.org> wrote:
> 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 +++++++++++++++++
Perhaps a new folio.h would be neater.
> @@ -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 > +}
It's a shame this isn't called folio_something(), like the rest of the API.
Unclear what this does. Some comments would help.
> +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); > +}
Why size_t? That's pretty rare in this space and I'd have expected unsigned long.
> @@ -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; > +}
What purpose does the READ_ONCE() serve?
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