#ifndef _LINUX_RMAP_H
  #define _LINUX_RMAP_H
  /*
   * Declarations for Reverse Mapping functions in mm/rmap.c
   */
  
  #include <linux/list.h>
  #include <linux/slab.h>
  #include <linux/mm.h>
  #include <linux/rwsem.h>
  #include <linux/memcontrol.h>
  
  /*
   * The anon_vma heads a list of private "related" vmas, to scan if
   * an anonymous page pointing to this anon_vma needs to be unmapped:
   * the vmas on the list will be related by forking, or by splitting.
   *
   * Since vmas come and go as they are split and merged (particularly
   * in mprotect), the mapping field of an anonymous page cannot point
   * directly to a vma: instead it points to an anon_vma, on whose list
   * the related vmas can be easily linked or unlinked.
   *
   * After unlinking the last vma on the list, we must garbage collect
   * the anon_vma object itself: we're guaranteed no page can be
   * pointing to this anon_vma once its vma list is empty.
   */
  struct anon_vma {
  	struct anon_vma *root;		/* Root of this anon_vma tree */
  	struct rw_semaphore rwsem;	/* W: modification, R: walking the list */
  	/*
  	 * The refcount is taken on an anon_vma when there is no
  	 * guarantee that the vma of page tables will exist for
  	 * the duration of the operation. A caller that takes
  	 * the reference is responsible for clearing up the
  	 * anon_vma if they are the last user on release
  	 */
  	atomic_t refcount;
  
  	/*
  	 * NOTE: the LSB of the rb_root.rb_node is set by
  	 * mm_take_all_locks() _after_ taking the above lock. So the
  	 * rb_root must only be read/written after taking the above lock
  	 * to be sure to see a valid next pointer. The LSB bit itself
  	 * is serialized by a system wide lock only visible to
  	 * mm_take_all_locks() (mm_all_locks_mutex).
  	 */
  	struct rb_root rb_root;	/* Interval tree of private "related" vmas */
  };
  
  /*
   * The copy-on-write semantics of fork mean that an anon_vma
   * can become associated with multiple processes. Furthermore,
   * each child process will have its own anon_vma, where new
   * pages for that process are instantiated.
   *
   * This structure allows us to find the anon_vmas associated
   * with a VMA, or the VMAs associated with an anon_vma.
   * The "same_vma" list contains the anon_vma_chains linking
   * all the anon_vmas associated with this VMA.
   * The "rb" field indexes on an interval tree the anon_vma_chains
   * which link all the VMAs associated with this anon_vma.
   */
  struct anon_vma_chain {
  	struct vm_area_struct *vma;
  	struct anon_vma *anon_vma;
  	struct list_head same_vma;   /* locked by mmap_sem & page_table_lock */
  	struct rb_node rb;			/* locked by anon_vma->rwsem */
  	unsigned long rb_subtree_last;
  #ifdef CONFIG_DEBUG_VM_RB
  	unsigned long cached_vma_start, cached_vma_last;
  #endif
  };
  
  enum ttu_flags {
  	TTU_UNMAP = 0,			/* unmap mode */
  	TTU_MIGRATION = 1,		/* migration mode */
  	TTU_MUNLOCK = 2,		/* munlock mode */
  	TTU_ACTION_MASK = 0xff,
  
  	TTU_IGNORE_MLOCK = (1 << 8),	/* ignore mlock */
  	TTU_IGNORE_ACCESS = (1 << 9),	/* don't age */
  	TTU_IGNORE_HWPOISON = (1 << 10),/* corrupted page is recoverable */
  };
  
  #ifdef CONFIG_MMU
  static inline void get_anon_vma(struct anon_vma *anon_vma)
  {
  	atomic_inc(&anon_vma->refcount);
  }
  
  void __put_anon_vma(struct anon_vma *anon_vma);
  
  static inline void put_anon_vma(struct anon_vma *anon_vma)
  {
  	if (atomic_dec_and_test(&anon_vma->refcount))
  		__put_anon_vma(anon_vma);
  }
  
  static inline struct anon_vma *page_anon_vma(struct page *page)
  {
  	if (((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) !=
  					    PAGE_MAPPING_ANON)
  		return NULL;
  	return page_rmapping(page);
  }
  
  static inline void vma_lock_anon_vma(struct vm_area_struct *vma)
  {
  	struct anon_vma *anon_vma = vma->anon_vma;
  	if (anon_vma)
  		down_write(&anon_vma->root->rwsem);
  }
  
  static inline void vma_unlock_anon_vma(struct vm_area_struct *vma)
  {
  	struct anon_vma *anon_vma = vma->anon_vma;
  	if (anon_vma)
  		up_write(&anon_vma->root->rwsem);
  }
  
  static inline void anon_vma_lock_write(struct anon_vma *anon_vma)
  {
  	down_write(&anon_vma->root->rwsem);
  }
  
  static inline void anon_vma_unlock_write(struct anon_vma *anon_vma)
  {
  	up_write(&anon_vma->root->rwsem);
  }
  
  static inline void anon_vma_lock_read(struct anon_vma *anon_vma)
  {
  	down_read(&anon_vma->root->rwsem);
  }
  
  static inline void anon_vma_unlock_read(struct anon_vma *anon_vma)
  {
  	up_read(&anon_vma->root->rwsem);
  }
  
  
  /*
   * anon_vma helper functions.
   */
  void anon_vma_init(void);	/* create anon_vma_cachep */
  int  anon_vma_prepare(struct vm_area_struct *);
  void unlink_anon_vmas(struct vm_area_struct *);
  int anon_vma_clone(struct vm_area_struct *, struct vm_area_struct *);
  int anon_vma_fork(struct vm_area_struct *, struct vm_area_struct *);
  
  static inline void anon_vma_merge(struct vm_area_struct *vma,
  				  struct vm_area_struct *next)
  {
  	VM_BUG_ON(vma->anon_vma != next->anon_vma);
  	unlink_anon_vmas(next);
  }
  
  struct anon_vma *page_get_anon_vma(struct page *page);
  
  /*
   * rmap interfaces called when adding or removing pte of page
   */
  void page_move_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
  void page_add_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
  void do_page_add_anon_rmap(struct page *, struct vm_area_struct *,
  			   unsigned long, int);
  void page_add_new_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
  void page_add_file_rmap(struct page *);
  void page_remove_rmap(struct page *);
  
  void hugepage_add_anon_rmap(struct page *, struct vm_area_struct *,
  			    unsigned long);
  void hugepage_add_new_anon_rmap(struct page *, struct vm_area_struct *,
  				unsigned long);
  
  static inline void page_dup_rmap(struct page *page)
  {
  	atomic_inc(&page->_mapcount);
  }
  
  /*
   * Called from mm/vmscan.c to handle paging out
   */
  int page_referenced(struct page *, int is_locked,
  			struct mem_cgroup *memcg, unsigned long *vm_flags);
  int page_referenced_one(struct page *, struct vm_area_struct *,
  	unsigned long address, void *arg);
  
  #define TTU_ACTION(x) ((x) & TTU_ACTION_MASK)
  
  int try_to_unmap(struct page *, enum ttu_flags flags);
  int try_to_unmap_one(struct page *, struct vm_area_struct *,
  			unsigned long address, void *arg);
  
  /*
   * Called from mm/filemap_xip.c to unmap empty zero page
   */
  pte_t *__page_check_address(struct page *, struct mm_struct *,
  				unsigned long, spinlock_t **, int);
  
  static inline pte_t *page_check_address(struct page *page, struct mm_struct *mm,
  					unsigned long address,
  					spinlock_t **ptlp, int sync)
  {
  	pte_t *ptep;
  
  	__cond_lock(*ptlp, ptep = __page_check_address(page, mm, address,
  						       ptlp, sync));
  	return ptep;
  }
  
  /*
   * Used by swapoff to help locate where page is expected in vma.
   */
  unsigned long page_address_in_vma(struct page *, struct vm_area_struct *);
  
  /*
   * Cleans the PTEs of shared mappings.
   * (and since clean PTEs should also be readonly, write protects them too)
   *
   * returns the number of cleaned PTEs.
   */
  int page_mkclean(struct page *);
  
  /*
   * called in munlock()/munmap() path to check for other vmas holding
   * the page mlocked.
   */
  int try_to_munlock(struct page *);
  
  /*
   * Called by memory-failure.c to kill processes.
   */
  struct anon_vma *page_lock_anon_vma_read(struct page *page);
  void page_unlock_anon_vma_read(struct anon_vma *anon_vma);
  int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma);
  
  /*
   * rmap_walk_control: To control rmap traversing for specific needs
   *
   * arg: passed to rmap_one() and invalid_vma()
   * rmap_one: executed on each vma where page is mapped
   * done: for checking traversing termination condition
   * file_nonlinear: for handling file nonlinear mapping
   * anon_lock: for getting anon_lock by optimized way rather than default
   * invalid_vma: for skipping uninterested vma
   */
  struct rmap_walk_control {
  	void *arg;
  	int (*rmap_one)(struct page *page, struct vm_area_struct *vma,
  					unsigned long addr, void *arg);
  	int (*done)(struct page *page);
  	int (*file_nonlinear)(struct page *, struct address_space *, void *arg);
  	struct anon_vma *(*anon_lock)(struct page *page);
  	bool (*invalid_vma)(struct vm_area_struct *vma, void *arg);
  };
  
  int rmap_walk(struct page *page, struct rmap_walk_control *rwc);
  
  #else	/* !CONFIG_MMU */
  
  #define anon_vma_init()		do {} while (0)
  #define anon_vma_prepare(vma)	(0)
  #define anon_vma_link(vma)	do {} while (0)
  
  static inline int page_referenced(struct page *page, int is_locked,
  				  struct mem_cgroup *memcg,
  				  unsigned long *vm_flags)
  {
  	*vm_flags = 0;
  	return 0;
  }
  
  #define try_to_unmap(page, refs) SWAP_FAIL
  
  static inline int page_mkclean(struct page *page)
  {
  	return 0;
  }
  
  
  #endif	/* CONFIG_MMU */
  
  /*
   * Return values of try_to_unmap
   */
  #define SWAP_SUCCESS	0
  #define SWAP_AGAIN	1
  #define SWAP_FAIL	2
  #define SWAP_MLOCK	3
  
  #endif	/* _LINUX_RMAP_H */