The patch titled
Subject: mm: make compound_head const-preserving
has been added to the -mm tree. Its filename is
mm-make-compound_head-const-preserving.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-make-compound_head-const-preserving.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-make-compound_head-const-preserving.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Subject: mm: make compound_head const-preserving
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@xxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/page-flags.h | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
--- a/include/linux/page-flags.h~mm-make-compound_head-const-preserving
+++ a/include/linux/page-flags.h
@@ -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;
_
Patches currently in -mm which might be from willy@xxxxxxxxxxxxx are
mm-make-__dump_page-static.patch
mm-debug-factor-pagepoisoned-out-of-__dump_page.patch
mm-page_owner-constify-dump_page_owner.patch
mm-make-compound_head-const-preserving.patch
mm-constify-get_pfnblock_flags_mask-and-get_pfnblock_migratetype.patch
mm-constify-page_count-and-page_ref_count.patch
