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Commit 4da1984e authored by Matthew Wilcox's avatar Matthew Wilcox Committed by Linus Torvalds
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mm: combine LRU and main union in struct page 

This gives us five words of space in a single union in struct page.  The
compound_mapcount moves position (from offset 24 to offset 20) on 64-bit
systems, but that does not seem likely to cause any trouble.

Link: http://lkml.kernel.org/r/20180518194519.3820-11-willy@infradead.org


Signed-off-by: default avatarMatthew Wilcox <mawilcox@microsoft.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarKirill 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b7ccc7f8

include/linux/mm_types.h

+46 −51
Original line number Diff line number Diff line
@@ -73,59 +73,19 @@ struct page { 
	unsigned long flags;		/* Atomic flags, some possibly

					 * updated asynchronously */

	/*

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

	 * the rest users of the storage space MUST NOT use the bit to

	 * Five words (20/40 bytes) are available in this union.

	 * WARNING: bit 0 of the first word is used for PageTail(). That

	 * means the other users of this union MUST NOT use the bit to

	 * avoid collision and false-positive PageTail().

	 */

	union {

		struct list_head lru;	/* Pageout list, eg. active_list

					 * protected by zone_lru_lock !

					 * Can be used as a generic list

		struct {	/* Page cache and anonymous pages */

			/**

			 * @lru: Pageout list, eg. active_list protected by

			 * zone_lru_lock.  Sometimes used as a generic list

			 * by the page owner.

			 */

		struct dev_pagemap *pgmap; /* ZONE_DEVICE pages are never on an

					    * lru or handled by a slab

					    * allocator, this points to the

					    * hosting device page map.

					    */

		struct {		/* slub per cpu partial pages */

			struct page *next;	/* Next partial slab */

#ifdef CONFIG_64BIT

			int pages;	/* Nr of partial slabs left */

			int pobjects;	/* Approximate # of objects */

#else

			short int pages;

			short int pobjects;

#endif

		};



		struct rcu_head rcu_head;	/* Used by SLAB

						 * when destroying via RCU

						 */

		/* Tail pages of compound page */

		struct {

			unsigned long compound_head; /* If bit zero is set */



			/* First tail page only */

			unsigned char compound_dtor;

			unsigned char compound_order;

			/* two/six bytes available here */

		};



#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS

		struct {

			unsigned long __pad;	/* do not overlay pmd_huge_pte

						 * with compound_head to avoid

						 * possible bit 0 collision.

						 */

			pgtable_t pmd_huge_pte; /* protected by page->ptl */

		};

#endif

	};



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

	union {

		struct {	/* Page cache and anonymous pages */

			struct list_head lru;

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

			struct address_space *mapping;

			pgoff_t index;		/* Our offset within mapping. */
@@ -138,6 +98,19 @@ struct page { 
			unsigned long private;

		};

		struct {	/* slab, slob and slub */

			union {

				struct list_head slab_list;	/* uses lru */

				struct {	/* Partial pages */

					struct page *next;

#ifdef CONFIG_64BIT

					int pages;	/* Nr of pages left */

					int pobjects;	/* Approximate count */

#else

					short int pages;

					short int pobjects;

#endif

				};

			};

			struct kmem_cache *slab_cache; /* not slob */

			/* Double-word boundary */

			void *freelist;		/* first free object */
@@ -151,9 +124,22 @@ struct page { 
				};

			};

		};

		atomic_t compound_mapcount;	/* first tail page */

		struct list_head deferred_list; /* second tail page */

		struct {	/* Tail pages of compound page */

			unsigned long compound_head;	/* Bit zero is set */



			/* First tail page only */

			unsigned char compound_dtor;

			unsigned char compound_order;

			atomic_t compound_mapcount;

		};

		struct {	/* Second tail page of compound page */

			unsigned long _compound_pad_1;	/* compound_head */

			unsigned long _compound_pad_2;

			struct list_head deferred_list;

		};

		struct {	/* Page table pages */

			unsigned long _pt_pad_1;	/* compound_head */

			pgtable_t pmd_huge_pte; /* protected by page->ptl */

			unsigned long _pt_pad_2;	/* mapping */

			unsigned long _pt_pad_3;

#if ALLOC_SPLIT_PTLOCKS
@@ -162,6 +148,15 @@ struct page { 
			spinlock_t ptl;

#endif

		};



		/** @rcu_head: You can use this to free a page by RCU. */

		struct rcu_head rcu_head;



		/**

		 * @pgmap: For ZONE_DEVICE pages, this points to the hosting

		 * device page map.

		 */

		struct dev_pagemap *pgmap;

	};



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

mm/page_alloc.c

+1 −1
Original line number Diff line number Diff line
@@ -943,7 +943,7 @@ static int free_tail_pages_check(struct page *head_page, struct page *page) 
	}

	switch (page - head_page) {

	case 1:

		/* the first tail page: ->mapping is compound_mapcount() */

		/* the first tail page: ->mapping may be compound_mapcount() */

		if (unlikely(compound_mapcount(page))) {

			bad_page(page, "nonzero compound_mapcount", 0);

			goto out;