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Commit 66a6ffd2 authored by Matthew Wilcox's avatar Matthew Wilcox Committed by Linus Torvalds
Browse files

mm: combine first three unions in struct page 

By combining these three one-word unions into one three-word union, we
make it easier for users to add their own multi-word fields to struct
page, as well as making it obvious that SLUB needs to keep its double-word
alignment for its freelist & counters.

No field moves position; verified with pahole.

Link: http://lkml.kernel.org/r/20180518194519.3820-8-willy@infradead.org


Signed-off-by: default avatarMatthew Wilcox <mawilcox@microsoft.com>
Acked-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b21999da

include/linux/mm_types.h

+33 −33
Original line number Diff line number Diff line
@@ -70,41 +70,28 @@ struct hmm; 
#endif



struct page {

	/* First double word block */

	unsigned long flags;		/* Atomic flags, some possibly

					 * updated asynchronously */

	/* Three words (12/24 bytes) are available in this union. */

	union {

		/* See page-flags.h for the definition of PAGE_MAPPING_FLAGS */

		struct {	/* Page cache and anonymous pages */

			/* See page-flags.h for PAGE_MAPPING_FLAGS */

			struct address_space *mapping;



		struct kmem_cache *slab_cache;	/* SL[AU]B: Pointer to slab */

		atomic_t compound_mapcount;	/* first tail page */

		/* page_deferred_list().next	 -- second tail page */

	};



	/* Second double word */

	union {

			pgoff_t index;		/* Our offset within mapping. */

		void *freelist;		/* sl[aou]b first free object */

		/* page_deferred_list().prev	-- second tail page */

	};



	union {

		/*

		 * Mapping-private opaque data:

		 * Usually used for buffer_heads if PagePrivate

		 * Used for swp_entry_t if PageSwapCache

		 * Indicates order in the buddy system if PageBuddy

			/**

			 * @private: Mapping-private opaque data.

			 * Usually used for buffer_heads if PagePrivate.

			 * Used for swp_entry_t if PageSwapCache.

			 * Indicates order in the buddy system if PageBuddy.

			 */

			unsigned long private;

#if USE_SPLIT_PTE_PTLOCKS

#if ALLOC_SPLIT_PTLOCKS

		spinlock_t *ptl;

#else

		spinlock_t ptl;

#endif

#endif

		void *s_mem;			/* slab first object */

		};

		struct {	/* slab, slob and slub */

			struct kmem_cache *slab_cache; /* not slob */

			/* Double-word boundary */

			void *freelist;		/* first free object */

			union {

				void *s_mem;	/* slab: first object */

				unsigned long counters;		/* SLUB */

				struct {			/* SLUB */

					unsigned inuse:16;
@@ -112,6 +99,19 @@ struct page { 
					unsigned frozen:1;

				};

			};

		};

		atomic_t compound_mapcount;	/* first tail page */

		struct list_head deferred_list; /* second tail page */

		struct {	/* Page table pages */

			unsigned long _pt_pad_2;	/* mapping */

			unsigned long _pt_pad_3;

#if ALLOC_SPLIT_PTLOCKS

			spinlock_t *ptl;

#else

			spinlock_t ptl;

#endif

		};

	};



	union {		/* This union is 4 bytes in size. */

		/*