#ifndef __LINUX_KSM_H
  #define __LINUX_KSM_H
  /*
   * Memory merging support.
   *
   * This code enables dynamic sharing of identical pages found in different
   * memory areas, even if they are not shared by fork().
   */
  
  #include <linux/bitops.h>
  #include <linux/mm.h>

  #include <linux/pagemap.h>
  #include <linux/rmap.h>

  #include <linux/sched.h>

  struct stable_node;

  struct mem_cgroup;

  struct page *ksm_does_need_to_copy(struct page *page,
  			struct vm_area_struct *vma, unsigned long address);

  #ifdef CONFIG_KSM
  int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
  		unsigned long end, int advice, unsigned long *vm_flags);
  int __ksm_enter(struct mm_struct *mm);

  void __ksm_exit(struct mm_struct *mm);

  
  static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
  {
  	if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags))
  		return __ksm_enter(mm);
  	return 0;
  }

  static inline void ksm_exit(struct mm_struct *mm)

  {
  	if (test_bit(MMF_VM_MERGEABLE, &mm->flags))

  		__ksm_exit(mm);

  }

  
  /*
   * A KSM page is one of those write-protected "shared pages" or "merged pages"
   * which KSM maps into multiple mms, wherever identical anonymous page content

   * is found in VM_MERGEABLE vmas.  It's a PageAnon page, pointing not to any
   * anon_vma, but to that page's node of the stable tree.

   */
  static inline int PageKsm(struct page *page)
  {

  	return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
  				(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);

  }

  static inline struct stable_node *page_stable_node(struct page *page)
  {
  	return PageKsm(page) ? page_rmapping(page) : NULL;
  }
  
  static inline void set_page_stable_node(struct page *page,
  					struct stable_node *stable_node)
  {
  	page->mapping = (void *)stable_node +
  				(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
  }

  /*
   * When do_swap_page() first faults in from swap what used to be a KSM page,
   * no problem, it will be assigned to this vma's anon_vma; but thereafter,
   * it might be faulted into a different anon_vma (or perhaps to a different
   * offset in the same anon_vma).  do_swap_page() cannot do all the locking
   * needed to reconstitute a cross-anon_vma KSM page: for now it has to make
   * a copy, and leave remerging the pages to a later pass of ksmd.
   *
   * We'd like to make this conditional on vma->vm_flags & VM_MERGEABLE,
   * but what if the vma was unmerged while the page was swapped out?
   */

  static inline int ksm_might_need_to_copy(struct page *page,

  			struct vm_area_struct *vma, unsigned long address)

  {

  	struct anon_vma *anon_vma = page_anon_vma(page);

  	return anon_vma &&
  		(anon_vma->root != vma->anon_vma->root ||
  		 page->index != linear_page_index(vma, address));

  }

  
  int page_referenced_ksm(struct page *page,
  			struct mem_cgroup *memcg, unsigned long *vm_flags);
  int try_to_unmap_ksm(struct page *page, enum ttu_flags flags);

  int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
  		  struct vm_area_struct *, unsigned long, void *), void *arg);
  void ksm_migrate_page(struct page *newpage, struct page *oldpage);

  #else  /* !CONFIG_KSM */

  static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
  {
  	return 0;
  }

  static inline void ksm_exit(struct mm_struct *mm)

  {
  }

  
  static inline int PageKsm(struct page *page)
  {
  	return 0;
  }

  #ifdef CONFIG_MMU
  static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
  		unsigned long end, int advice, unsigned long *vm_flags)
  {
  	return 0;
  }

  static inline int ksm_might_need_to_copy(struct page *page,

  			struct vm_area_struct *vma, unsigned long address)
  {

  	return 0;

  }
  
  static inline int page_referenced_ksm(struct page *page,
  			struct mem_cgroup *memcg, unsigned long *vm_flags)
  {
  	return 0;
  }
  
  static inline int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
  {
  	return 0;
  }

  
  static inline int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page*,
  		struct vm_area_struct *, unsigned long, void *), void *arg)
  {
  	return 0;
  }
  
  static inline void ksm_migrate_page(struct page *newpage, struct page *oldpage)
  {
  }

  #endif /* CONFIG_MMU */

  #endif /* !CONFIG_KSM */

  #endif /* __LINUX_KSM_H */