From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id EA70D6B0024 for ; Wed, 18 Apr 2018 14:49:27 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id j25so1381831pfh.18 for ; Wed, 18 Apr 2018 11:49:27 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2607:7c80:54:e::133]) by mx.google.com with ESMTPS id f8si1481332pgt.243.2018.04.18.11.49.23 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 18 Apr 2018 11:49:23 -0700 (PDT) From: Matthew Wilcox Subject: [PATCH v3 08/14] mm: Combine first three unions in struct page Date: Wed, 18 Apr 2018 11:49:06 -0700 Message-Id: <20180418184912.2851-9-willy@infradead.org> In-Reply-To: <20180418184912.2851-1-willy@infradead.org> References: <20180418184912.2851-1-willy@infradead.org> Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org Cc: Matthew Wilcox , Andrew Morton , "Kirill A . Shutemov" , Christoph Lameter , Lai Jiangshan , Pekka Enberg , Vlastimil Babka From: Matthew Wilcox 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 --- include/linux/mm_types.h | 65 ++++++++++++++++++++-------------------- 1 file changed, 32 insertions(+), 33 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 04d9dc442029..39521b8385c1 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -70,45 +70,44 @@ struct hmm; #endif struct page { - /* First double word block */ unsigned long flags; /* Atomic flags, some possibly * updated asynchronously */ - 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 */ + union { /* This union is three words (12/24 bytes) in size */ + 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 and slob */ + struct kmem_cache *slab_cache; + void *freelist; /* first free object */ + void *s_mem; /* first object */ + }; + struct { /* slub also uses some of the slab fields */ + struct kmem_cache *slub_cache; + /* Double-word boundary */ + void *slub_freelist; + 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 _ptl_pad_1; + unsigned long _ptl_pad_2; #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 */ - struct { /* SLUB */ - unsigned inuse:16; - unsigned objects:15; - unsigned frozen:1; }; }; -- 2.17.0