/*
   * swapcache pages are stored in the swapper_space radix tree.  We want to
   * get good packing density in that tree, so the index should be dense in
   * the low-order bits.
   *
   * We arrange the `type' and `offset' fields so that `type' is at the five

   * high-order bits of the swp_entry_t and `offset' is right-aligned in the

   * remaining bits.
   *
   * swp_entry_t's are *never* stored anywhere in their arch-dependent format.
   */
  #define SWP_TYPE_SHIFT(e)	(sizeof(e.val) * 8 - MAX_SWAPFILES_SHIFT)
  #define SWP_OFFSET_MASK(e)	((1UL << SWP_TYPE_SHIFT(e)) - 1)
  
  /*
   * Store a type+offset into a swp_entry_t in an arch-independent format
   */
  static inline swp_entry_t swp_entry(unsigned long type, pgoff_t offset)
  {
  	swp_entry_t ret;
  
  	ret.val = (type << SWP_TYPE_SHIFT(ret)) |
  			(offset & SWP_OFFSET_MASK(ret));
  	return ret;
  }
  
  /*
   * Extract the `type' field from a swp_entry_t.  The swp_entry_t is in
   * arch-independent format
   */
  static inline unsigned swp_type(swp_entry_t entry)
  {
  	return (entry.val >> SWP_TYPE_SHIFT(entry));
  }
  
  /*
   * Extract the `offset' field from a swp_entry_t.  The swp_entry_t is in
   * arch-independent format
   */
  static inline pgoff_t swp_offset(swp_entry_t entry)
  {
  	return entry.val & SWP_OFFSET_MASK(entry);
  }

  #ifdef CONFIG_MMU

  /* check whether a pte points to a swap entry */
  static inline int is_swap_pte(pte_t pte)
  {
  	return !pte_none(pte) && !pte_present(pte) && !pte_file(pte);
  }

  #endif

  /*
   * Convert the arch-dependent pte representation of a swp_entry_t into an
   * arch-independent swp_entry_t.
   */
  static inline swp_entry_t pte_to_swp_entry(pte_t pte)
  {
  	swp_entry_t arch_entry;
  
  	BUG_ON(pte_file(pte));
  	arch_entry = __pte_to_swp_entry(pte);
  	return swp_entry(__swp_type(arch_entry), __swp_offset(arch_entry));
  }
  
  /*
   * Convert the arch-independent representation of a swp_entry_t into the
   * arch-dependent pte representation.
   */
  static inline pte_t swp_entry_to_pte(swp_entry_t entry)
  {
  	swp_entry_t arch_entry;
  
  	arch_entry = __swp_entry(swp_type(entry), swp_offset(entry));
  	BUG_ON(pte_file(__swp_entry_to_pte(arch_entry)));
  	return __swp_entry_to_pte(arch_entry);
  }

  
  #ifdef CONFIG_MIGRATION
  static inline swp_entry_t make_migration_entry(struct page *page, int write)
  {
  	BUG_ON(!PageLocked(page));
  	return swp_entry(write ? SWP_MIGRATION_WRITE : SWP_MIGRATION_READ,
  			page_to_pfn(page));
  }
  
  static inline int is_migration_entry(swp_entry_t entry)
  {
  	return unlikely(swp_type(entry) == SWP_MIGRATION_READ ||
  			swp_type(entry) == SWP_MIGRATION_WRITE);
  }
  
  static inline int is_write_migration_entry(swp_entry_t entry)
  {
  	return unlikely(swp_type(entry) == SWP_MIGRATION_WRITE);
  }
  
  static inline struct page *migration_entry_to_page(swp_entry_t entry)
  {
  	struct page *p = pfn_to_page(swp_offset(entry));
  	/*
  	 * Any use of migration entries may only occur while the
  	 * corresponding page is locked
  	 */
  	BUG_ON(!PageLocked(p));
  	return p;
  }
  
  static inline void make_migration_entry_read(swp_entry_t *entry)
  {
  	*entry = swp_entry(SWP_MIGRATION_READ, swp_offset(*entry));
  }
  
  extern void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
  					unsigned long address);
  #else
  
  #define make_migration_entry(page, write) swp_entry(0, 0)

  static inline int is_migration_entry(swp_entry_t swp)
  {
  	return 0;
  }

  #define migration_entry_to_page(swp) NULL
  static inline void make_migration_entry_read(swp_entry_t *entryp) { }
  static inline void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
  					 unsigned long address) { }
  static inline int is_write_migration_entry(swp_entry_t entry)
  {
  	return 0;
  }
  
  #endif

  #ifdef CONFIG_MEMORY_FAILURE
  /*
   * Support for hardware poisoned pages
   */
  static inline swp_entry_t make_hwpoison_entry(struct page *page)
  {
  	BUG_ON(!PageLocked(page));
  	return swp_entry(SWP_HWPOISON, page_to_pfn(page));
  }
  
  static inline int is_hwpoison_entry(swp_entry_t entry)
  {
  	return swp_type(entry) == SWP_HWPOISON;
  }
  #else
  
  static inline swp_entry_t make_hwpoison_entry(struct page *page)
  {
  	return swp_entry(0, 0);
  }
  
  static inline int is_hwpoison_entry(swp_entry_t swp)
  {
  	return 0;
  }
  #endif
  
  #if defined(CONFIG_MEMORY_FAILURE) || defined(CONFIG_MIGRATION)
  static inline int non_swap_entry(swp_entry_t entry)
  {
  	return swp_type(entry) >= MAX_SWAPFILES;
  }
  #else
  static inline int non_swap_entry(swp_entry_t entry)
  {
  	return 0;
  }
  #endif