struct page*

struct page {
        unsigned long flags;            /* Atomic flags, some possibly
                                         * updated asynchronously */
        atomic_t _count;                /* Usage count, see below. */
        union {
                atomic_t _mapcount;     /* Count of ptes mapped in mms,
                                         * to show when page is mapped
                                         * & limit reverse map searches.
                                         */
                struct {                /* SLUB */
                        u16 inuse;
                        u16 objects;
                };
        };
        union {
            struct {
                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.
                                                 */
                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:
                                                 * see PAGE_MAPPING_ANON below.
                                                 */
            };
#if USE_SPLIT_PTLOCKS
            spinlock_t ptl;
#endif
            struct kmem_cache *slab;    /* SLUB: Pointer to slab */
            struct page *first_page;    /* Compound tail pages */
        };
        union {
                pgoff_t index;          /* Our offset within mapping. */
                void *freelist;         /* SLUB: freelist req. slab lock */
        };
        struct list_head lru;           /* Pageout list, eg. active_list
                                         * protected by zone->lru_lock !
                                         */
        /*
         * On machines where all RAM is mapped into kernel address space,
         * we can simply calculate the virtual address. On machines with
         * highmem some memory is mapped into kernel virtual memory
         * dynamically, so we need a place to store that address.
         * Note that this field could be 16 bits on x86 ... ;)
         *
         * Architectures with slow multiplication can define
         * WANT_PAGE_VIRTUAL in asm/page.h
         */
#if defined(WANT_PAGE_VIRTUAL)
        void *virtual;                  /* Kernel virtual address (NULL if
                                           not kmapped, ie. highmem) */
#endif /* WANT_PAGE_VIRTUAL */
#ifdef CONFIG_WANT_PAGE_DEBUG_FLAGS
        unsigned long debug_flags;      /* Use atomic bitops on this */
#endif

#ifdef CONFIG_KMEMCHECK
        /*
         * kmemcheck wants to track the status of each byte in a page; this
         * is a pointer to such a status block. NULL if not tracked.
         */
        void *shadow;
#endif
};

/*
 * A region containing a mapping of a non-memory backed file under NOMMU
 * conditions.  These are held in a global tree and are pinned by the VMAs that
 * map parts of them.
 */
struct vm_region {
        struct rb_node  vm_rb;          /* link in global region tree */
        unsigned long   vm_flags;       /* VMA vm_flags */
        unsigned long   vm_start;       /* start address of region */
        unsigned long   vm_end;         /* region initialised to here */
        unsigned long   vm_top;         /* region allocated to here */
        unsigned long   vm_pgoff;       /* the offset in vm_file corresponding to vm_start */
        struct file     *vm_file;       /* the backing file or NULL */

        int             vm_usage;       /* region usage count (access under nommu_region_sem) */
        bool            vm_icache_flushed : 1; /* true if the icache has been flushed for
                                                * this region */
};

　　1 unsigned long flags

unsigned long flags
//flags在page-flags.h文件夹中枚举
//paging_init()可设置PG_reserved做flags
//mem_init()可设置含PG_reserved的flags清除
//#define PG_reserved 11;表示页保留，无法被__free_page()回收

　　2 atomic_t _count和atumic_t _mapcount 

atomic_t _count;          //页引用计数器
atomic_t _mapcount;    //页映射计数器
//paging_init()可以将它们初始化为-1
//mem_init()可以将所有位码为0的页的_count设置为0
//page_count和page_mapcount可以统计其实用者个数
//_count+1为页使用者个数，_mapcount+1为页共享者个数
// _count为-1时不可被__free_page()释放
//_mapcount为0表示该页未被共享

　　3 unsigned long private

unsigned long private;        //私有数据指针
//设置为PG_private，则private字段指向struct buffer_head
//设置为PG_compound，则指向struct page
//设置为PG_swapcache，则private为swp_entry_t的成员变量val

　　4 struct address_space *mapping

struct address_space *mapping；  //该页所在地址空间描述结构指针
/*page->mapping == 0 属于交换高速缓存页
*page->mapping != 0 且第0位为1，为匿名页，指向struct anon_vma
*page->mapping != 0 且第0位为0，指向struct address_space地址空间结构变量
*/

　　5 pgoff_t index

pgoff_t index; 
//该页描述结构在地址空间radix树page_tree中的对象索引号即页号
//表示该页在vm_file中的便宜页数
//#define unsigned long pgoff_t

　　6 struct list_head lru

struct list_head lru; //最近、最久未使用struct slab结构指针变量
//设置PG_slab，则该页由slab分配器来管理，lru.next指向kmem_cache_t结构变量，lru.prev则指向struct slab结构

　　7 struct pagevec

struct pagevec {                //页向量描述结构
        unsigned long nr;       //该页向量中的内存页数
        unsigned long cold;    //冷区标志，0表示热区，非0表示冷区
        struct page *pages[PAGEVEC_SIZE];
        //该也想两种的页描述结构指针数组（PAGEVEC_SIZE=14）
};

　　8 struct page_address_map

struct page_address_map {        //页地址映射
        struct page *page;            //页的描述结构
        void *virtual;                //页的虚拟地址
        struct list_head list;           //通过list字段链接到页表池全局链表page_address_pool中或page_address_htable[hash_ptr(page,PA_HASH_ORDER)].lh
};    

　　9 struct page_address_slot

static struct page_address_slot {
        struct list_head lh;                    /* List of page_address_maps */
        spinlock_t lock;                        /* Protect this bucket's list */
} ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];