We have trouble keeping track of whether we've already called
compound_head() to ensure we're not operating on a tail page. Further,
it's never clear whether we intend a struct page to refer to PAGE_SIZE
bytes or page_size(compound_head(page)).
Introduce a new type 'struct folio' that always refers to an entire
(possibly compound) page, and points to the head page (or base page).
Signed-off-by: Matthew Wilcox (Oracle) <wi...@infradead.org>
---
include/linux/mm.h | 26 ++++++++++++++++++++++++++
include/linux/mm_types.h | 17 +++++++++++++++++
2 files changed, 43 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a5d618d08506..0858af6479a3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -924,6 +924,11 @@ 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)
{
/*
@@ -975,6 +980,26 @@ static inline unsigned int page_shift(struct page *page)
void free_compound_page(struct page *page);
+static inline unsigned long folio_nr_pages(struct folio *folio)
+{
+ return compound_nr(&folio->page);
+}
+
+static inline struct folio *next_folio(struct folio *folio)
+{
+ return folio + folio_nr_pages(folio);
+}
+
+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);
+}
+
#ifdef CONFIG_MMU
/*
* Do pte_mkwrite, but only if the vma says VM_WRITE. We do this when
@@ -1615,6 +1640,7 @@ 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 07d9acb5b19c..875dc6cd6ad2 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;
--
2.29.2
