[v9,05/96] mm: Make compound_head const-preserving
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Message ID 20210505150628.111735-6-willy@infradead.org
State New, archived
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  • Memory folios
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Commit Message

Matthew Wilcox May 5, 2021, 3:04 p.m. UTC
If you pass a const pointer to compound_head(), you get a const pointer
back; if you pass a mutable pointer, you get a mutable pointer back.
Also remove an unnecessary forward definition of struct page; we're about
to dereference page->compound_head, so it must already have been defined.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
 include/linux/page-flags.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

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diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 04a34c08e0a6..d8e26243db25 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -177,17 +177,17 @@  enum pageflags {
-struct page;	/* forward declaration */
-static inline struct page *compound_head(struct page *page)
+static inline unsigned long _compound_head(const struct page *page)
 	unsigned long head = READ_ONCE(page->compound_head);
 	if (unlikely(head & 1))
-		return (struct page *) (head - 1);
-	return page;
+		return head - 1;
+	return (unsigned long)page;
+#define compound_head(page)	((typeof(page))_compound_head(page))
 static __always_inline int PageTail(struct page *page)
 	return READ_ONCE(page->compound_head) & 1;