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mm: make compound_head const-preserving

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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.

Link: https://lkml.kernel.org/r/20210416231531.2521383-5-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2021-06-28 19:41:19 -07:00 committed by Linus Torvalds
parent 8bf6f451bd
commit 0f2317e34e
1 changed files with 5 additions and 5 deletions
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10
include/linux/page-flags.h
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@ -177,17 +177,17 @@ enum pageflags {
#ifndef __GENERATING_BOUNDS_H
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;