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mm: move _refcount out of struct page union 

Keeping the refcount in the union only encourages people to put something
else in the union which will overlap with _refcount and eventually explode
messily.  pahole reports no fields change location.

Link: http://lkml.kernel.org/r/20180518194519.3820-7-willy@infradead.org
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.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 2018-06-07 17:08:35 -07:00 committed by Linus Torvalds
parent 7d27a04bb2
commit b21999da02
1 changed files with 10 additions and 15 deletions
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25
include/linux/mm_types.h
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@ -113,7 +113,13 @@ struct page {
};
};
union {
union { /* This union is 4 bytes in size. */
/*
* If the page can be mapped to userspace, encodes the number
* of times this page is referenced by a page table.
*/
atomic_t _mapcount;
/*
* If the page is neither PageSlab nor mappable to userspace,
* the value stored here may help determine what this page
@ -124,22 +130,11 @@ struct page {
unsigned int active; /* SLAB */
int units; /* SLOB */
struct { /* Page cache */
/*
* Count of ptes mapped in mms, to show when
* page is mapped & limit reverse map searches.
*/
atomic_t _mapcount;
/*
* Usage count, *USE WRAPPER FUNCTION* when manual
* accounting. See page_ref.h
*/
atomic_t _refcount;
};
};
/* Usage count. *DO NOT USE DIRECTLY*. See page_ref.h */
atomic_t _refcount;
/*
* WARNING: bit 0 of the first word encode PageTail(). That means
* the rest users of the storage space MUST NOT use the bit to