text: /* SPDX-License-Identifier: GPL-2.0 */
  #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>
  #include <linux/sched/coredump.h>
  
  struct stable_node;
  struct mem_cgroup;
  
  #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);
  }
  
  /*
   * 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?
   */
  struct page *ksm_might_need_to_copy(struct page *page,
  			struct vm_area_struct *vma, unsigned long address);
  
  void rmap_walk_ksm(struct folio *folio, const struct rmap_walk_control *rwc);
  void folio_migrate_ksm(struct folio *newfolio, struct folio *folio);
  
  #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)
  {
  }
  
  #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 struct page *ksm_might_need_to_copy(struct page *page,
  			struct vm_area_struct *vma, unsigned long address)
  {
  	return page;
  }
  
  static inline void rmap_walk_ksm(struct folio *folio,
  			const struct rmap_walk_control *rwc)
  {
  }
  
  static inline void folio_migrate_ksm(struct folio *newfolio, struct folio *old)
  {
  }
  #endif /* CONFIG_MMU */
  #endif /* !CONFIG_KSM */
  
  #endif /* __LINUX_KSM_H */
  