diff options
Diffstat (limited to 'include/linux/mm_types.h')
| -rw-r--r-- | include/linux/mm_types.h | 154 |
1 files changed, 74 insertions, 80 deletions
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index cfd0ac4e5e0e..fd1af6b9591d 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -31,28 +31,56 @@ struct hmm; * it to keep track of whatever it is we are using the page for at the * moment. Note that we have no way to track which tasks are using * a page, though if it is a pagecache page, rmap structures can tell us - * who is mapping it. + * who is mapping it. If you allocate the page using alloc_pages(), you + * can use some of the space in struct page for your own purposes. * - * The objects in struct page are organized in double word blocks in - * order to allows us to use atomic double word operations on portions - * of struct page. That is currently only used by slub but the arrangement - * allows the use of atomic double word operations on the flags/mapping - * and lru list pointers also. + * Pages that were once in the page cache may be found under the RCU lock + * even after they have been recycled to a different purpose. The page + * cache reads and writes some of the fields in struct page to pin the + * page before checking that it's still in the page cache. It is vital + * that all users of struct page: + * 1. Use the first word as PageFlags. + * 2. Clear or preserve bit 0 of page->compound_head. It is used as + * PageTail for compound pages, and the page cache must not see false + * positives. Some users put a pointer here (guaranteed to be at least + * 4-byte aligned), other users avoid using the field altogether. + * 3. page->_refcount must either not be used, or must be used in such a + * way that other CPUs temporarily incrementing and then decrementing the + * refcount does not cause problems. On receiving the page from + * alloc_pages(), the refcount will be positive. + * 4. Either preserve page->_mapcount or restore it to -1 before freeing it. + * + * If you allocate pages of order > 0, you can use the fields in the struct + * page associated with each page, but bear in mind that the pages may have + * been inserted individually into the page cache, so you must use the above + * four fields in a compatible way for each struct page. + * + * SLUB uses cmpxchg_double() to atomically update its freelist and + * counters. That requires that freelist & counters be adjacent and + * double-word aligned. We align all struct pages to double-word + * boundaries, and ensure that 'freelist' is aligned within the + * struct. */ +#ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE +#define _struct_page_alignment __aligned(2 * sizeof(unsigned long)) +#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) +#define _slub_counter_t unsigned long +#else +#define _slub_counter_t unsigned int +#endif +#else /* !CONFIG_HAVE_ALIGNED_STRUCT_PAGE */ +#define _struct_page_alignment +#define _slub_counter_t unsigned int +#endif /* !CONFIG_HAVE_ALIGNED_STRUCT_PAGE */ + struct page { /* First double word block */ unsigned long flags; /* Atomic flags, some possibly * updated asynchronously */ union { - struct address_space *mapping; /* If low bit clear, points to - * inode address_space, or NULL. - * If page mapped as anonymous - * memory, low bit is set, and - * it points to anon_vma object - * or KSM private structure. See - * PAGE_MAPPING_ANON and - * PAGE_MAPPING_KSM. - */ + /* See page-flags.h for the definition of PAGE_MAPPING_FLAGS */ + struct address_space *mapping; + void *s_mem; /* slab first object */ atomic_t compound_mapcount; /* first tail page */ /* page_deferred_list().next -- second tail page */ @@ -66,40 +94,27 @@ struct page { }; union { -#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \ - defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) - /* Used for cmpxchg_double in slub */ - unsigned long counters; -#else - /* - * Keep _refcount separate from slub cmpxchg_double data. - * As the rest of the double word is protected by slab_lock - * but _refcount is not. - */ - unsigned counters; -#endif - struct { + _slub_counter_t counters; + unsigned int active; /* SLAB */ + struct { /* SLUB */ + unsigned inuse:16; + unsigned objects:15; + unsigned frozen:1; + }; + int units; /* SLOB */ + + struct { /* Page cache */ + /* + * Count of ptes mapped in mms, to show when + * page is mapped & limit reverse map searches. + * + * Extra information about page type may be + * stored here for pages that are never mapped, + * in which case the value MUST BE <= -2. + * See page-flags.h for more details. + */ + atomic_t _mapcount; - union { - /* - * Count of ptes mapped in mms, to show when - * page is mapped & limit reverse map searches. - * - * Extra information about page type may be - * stored here for pages that are never mapped, - * in which case the value MUST BE <= -2. - * See page-flags.h for more details. - */ - atomic_t _mapcount; - - unsigned int active; /* SLAB */ - struct { /* SLUB */ - unsigned inuse:16; - unsigned objects:15; - unsigned frozen:1; - }; - int units; /* SLOB */ - }; /* * Usage count, *USE WRAPPER FUNCTION* when manual * accounting. See page_ref.h @@ -109,8 +124,6 @@ struct page { }; /* - * Third double word block - * * WARNING: bit 0 of the first word encode PageTail(). That means * the rest users of the storage space MUST NOT use the bit to * avoid collision and false-positive PageTail(). @@ -145,19 +158,9 @@ struct page { unsigned long compound_head; /* If bit zero is set */ /* First tail page only */ -#ifdef CONFIG_64BIT - /* - * On 64 bit system we have enough space in struct page - * to encode compound_dtor and compound_order with - * unsigned int. It can help compiler generate better or - * smaller code on some archtectures. - */ - unsigned int compound_dtor; - unsigned int compound_order; -#else - unsigned short int compound_dtor; - unsigned short int compound_order; -#endif + unsigned char compound_dtor; + unsigned char compound_order; + /* two/six bytes available here */ }; #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS @@ -171,15 +174,14 @@ struct page { #endif }; - /* Remainder is not double word aligned */ union { - unsigned long private; /* Mapping-private opaque data: - * usually used for buffer_heads - * if PagePrivate set; used for - * swp_entry_t if PageSwapCache; - * indicates order in the buddy - * system if PG_buddy is set. - */ + /* + * 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; @@ -212,15 +214,7 @@ struct page { #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS int _last_cpupid; #endif -} -/* - * The struct page can be forced to be double word aligned so that atomic ops - * on double words work. The SLUB allocator can make use of such a feature. - */ -#ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE - __aligned(2 * sizeof(unsigned long)) -#endif -; +} _struct_page_alignment; #define PAGE_FRAG_CACHE_MAX_SIZE __ALIGN_MASK(32768, ~PAGE_MASK) #define PAGE_FRAG_CACHE_MAX_ORDER get_order(PAGE_FRAG_CACHE_MAX_SIZE) |