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电梯直达

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发表于 2009-10-30 10:24 |只看该作者 |倒序浏览

这是2.6.28内核中page结构的定义，其中的 atomic_t _mapcount作用是什么，注释没有看明白。谢谢。

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 */
};