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From: Matthew Wilcox <willy@infradead.org>
To: linux-mm@kvack.org
Cc: "Matthew Wilcox" <mawilcox@microsoft.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	"Christoph Lameter" <cl@linux.com>,
	"Lai Jiangshan" <jiangshanlai@gmail.com>,
	"Pekka Enberg" <penberg@kernel.org>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"Jérôme Glisse" <jglisse@redhat.com>
Subject: [PATCH v5 07/17] mm: Combine first three unions in struct page
Date: Fri,  4 May 2018 11:33:08 -0700	[thread overview]
Message-ID: <20180504183318.14415-8-willy@infradead.org> (raw)
In-Reply-To: <20180504183318.14415-1-willy@infradead.org>

From: Matthew Wilcox <mawilcox@microsoft.com>

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.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 include/linux/mm_types.h | 66 ++++++++++++++++++++--------------------
 1 file changed, 33 insertions(+), 33 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 9828cd170251..629a7b568ed7 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -70,46 +70,46 @@ 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 address_space *mapping;
-
-		struct kmem_cache *slab_cache;	/* SL[AU]B: Pointer to slab */
+		struct {	/* Page cache and anonymous pages */
+			/* See page-flags.h for PAGE_MAPPING_FLAGS */
+			struct address_space *mapping;
+			pgoff_t index;		/* Our offset within mapping. */
+			/**
+			 * @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;
+		};
+		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;
+					unsigned objects:15;
+					unsigned frozen:1;
+				};
+			};
+		};
 		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
-		 */
-		unsigned long private;
-#if USE_SPLIT_PTE_PTLOCKS
+		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;
+			spinlock_t *ptl;
 #else
-		spinlock_t ptl;
-#endif
+			spinlock_t ptl;
 #endif
-		void *s_mem;			/* slab first object */
-		unsigned long counters;		/* SLUB */
-		struct {			/* SLUB */
-			unsigned inuse:16;
-			unsigned objects:15;
-			unsigned frozen:1;
 		};
 	};
 
-- 
2.17.0

  parent reply	other threads:[~2018-05-04 18:33 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-04 18:33 [PATCH v5 00/17] Rearrange " Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 01/17] s390: Use _refcount for pgtables Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 02/17] mm: Split page_type out from _mapcount Matthew Wilcox
2018-05-14 14:33   ` Vlastimil Babka
2018-05-04 18:33 ` [PATCH v5 03/17] mm: Mark pages in use for page tables Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 04/17] mm: Switch s_mem and slab_cache in struct page Matthew Wilcox
2018-05-07 14:58   ` Christopher Lameter
2018-05-14 14:37   ` Vlastimil Babka
2018-05-04 18:33 ` [PATCH v5 05/17] mm: Move 'private' union within " Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 06/17] mm: Move _refcount out of struct page union Matthew Wilcox
2018-05-04 18:33 ` Matthew Wilcox [this message]
2018-05-14 14:42   ` [PATCH v5 07/17] mm: Combine first three unions in struct page Vlastimil Babka
2018-05-04 18:33 ` [PATCH v5 08/17] mm: Use page->deferred_list Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 09/17] mm: Move lru union within struct page Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 10/17] mm: Combine LRU and main union in " Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 11/17] mm: Improve struct page documentation Matthew Wilcox
2018-05-15  9:22   ` Vlastimil Babka
2018-05-04 18:33 ` [PATCH v5 12/17] mm: Add pt_mm to struct page Matthew Wilcox
2018-05-15  9:27   ` Vlastimil Babka
2018-05-15 12:23     ` Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 13/17] mm: Add hmm_data " Matthew Wilcox
2018-05-15  9:32   ` Vlastimil Babka
2018-05-15 12:40     ` Vlastimil Babka
2018-05-04 18:33 ` [PATCH v5 14/17] slab,slub: Remove rcu_head size checks Matthew Wilcox
2018-05-15 11:30   ` Vlastimil Babka
2018-05-04 18:33 ` [PATCH v5 15/17] slub: Remove kmem_cache->reserved Matthew Wilcox
2018-05-04 18:33 ` [PATCH v5 16/17] slub: Remove 'reserved' file from sysfs Matthew Wilcox
2018-05-07 15:01   ` Christopher Lameter
2018-05-04 18:33 ` [PATCH v5 17/17] mm: Distinguish VMalloc pages Matthew Wilcox
2018-05-04 20:52 ` [PATCH v5 00/17] Rearrange struct page Andrew Morton
2018-05-04 21:25   ` Matthew Wilcox

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