Commit b21999da authored Jun 07, 2018 by Matthew Wilcox Committed by Linus Torvalds Jun 07, 2018

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>

parent 7d27a04b

include/linux/mm_types.h

+10 −15

Original line number	Diff line number	Diff line
		@@ -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
		@@ -124,21 +130,10 @@ 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
		*/
		/* Usage count. DO NOT USE DIRECTLY. See page_ref.h */
		atomic_t _refcount;
		};
		};

		/*
		* WARNING: bit 0 of the first word encode PageTail(). That means