include/linux/ksm.h

   1 #ifndef __LINUX_KSM_H
   2 #define __LINUX_KSM_H
   3 /*
   4  * Memory merging support.
   5  *
   6  * This code enables dynamic sharing of identical pages found in different
   7  * memory areas, even if they are not shared by fork().
   8  */
   9
  10 #include <linux/bitops.h>
  11 #include <linux/mm.h>
  12 #include <linux/pagemap.h>
  13 #include <linux/rmap.h>
  14 #include <linux/sched.h>
  15
  16 struct stable_node;
  17 struct mem_cgroup;
  18
  19 #ifdef CONFIG_KSM
  20 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
  21                 unsigned long end, int advice, unsigned long *vm_flags);
  22 int __ksm_enter(struct mm_struct *mm);
  23 void __ksm_exit(struct mm_struct *mm);
  24
  25 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
  26 {
  27         if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags))
  28                 return __ksm_enter(mm);
  29         return 0;
  30 }
  31
  32 static inline void ksm_exit(struct mm_struct *mm)
  33 {
  34         if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
  35                 __ksm_exit(mm);
  36 }
  37
  38 /*
  39  * A KSM page is one of those write-protected "shared pages" or "merged pages"
  40  * which KSM maps into multiple mms, wherever identical anonymous page content
  41  * is found in VM_MERGEABLE vmas.  It's a PageAnon page, pointing not to any
  42  * anon_vma, but to that page's node of the stable tree.
  43  */
  44 static inline int PageKsm(struct page *page)
  45 {
  46         return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
  47                                 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
  48 }
  49
  50 static inline struct stable_node *page_stable_node(struct page *page)
  51 {
  52         return PageKsm(page) ? page_rmapping(page) : NULL;
  53 }
  54
  55 static inline void set_page_stable_node(struct page *page,
  56                                         struct stable_node *stable_node)
  57 {
  58         page->mapping = (void *)stable_node +
  59                                 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
  60 }
  61
  62 /*
  63  * When do_swap_page() first faults in from swap what used to be a KSM page,
  64  * no problem, it will be assigned to this vma's anon_vma; but thereafter,
  65  * it might be faulted into a different anon_vma (or perhaps to a different
  66  * offset in the same anon_vma).  do_swap_page() cannot do all the locking
  67  * needed to reconstitute a cross-anon_vma KSM page: for now it has to make
  68  * a copy, and leave remerging the pages to a later pass of ksmd.
  69  *
  70  * We'd like to make this conditional on vma->vm_flags & VM_MERGEABLE,
  71  * but what if the vma was unmerged while the page was swapped out?
  72  */
  73 struct page *ksm_does_need_to_copy(struct page *page,
  74                         struct vm_area_struct *vma, unsigned long address);
  75 static inline struct page *ksm_might_need_to_copy(struct page *page,
  76                         struct vm_area_struct *vma, unsigned long address)
  77 {
  78         struct anon_vma *anon_vma = page_anon_vma(page);
  79
  80         if (!anon_vma ||
  81             (anon_vma == vma->anon_vma &&
  82              page->index == linear_page_index(vma, address)))
  83                 return page;
  84
  85         return ksm_does_need_to_copy(page, vma, address);
  86 }
  87
  88 int page_referenced_ksm(struct page *page,
  89                         struct mem_cgroup *memcg, unsigned long *vm_flags);
  90 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags);
  91 int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
  92                   struct vm_area_struct *, unsigned long, void *), void *arg);
  93 void ksm_migrate_page(struct page *newpage, struct page *oldpage);
  94
  95 #else  /* !CONFIG_KSM */
  96
  97 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
  98 {
  99         return 0;
 100 }
 101
 102 static inline void ksm_exit(struct mm_struct *mm)
 103 {
 104 }
 105
 106 static inline int PageKsm(struct page *page)
 107 {
 108         return 0;
 109 }
 110
 111 #ifdef CONFIG_MMU
 112 static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 113                 unsigned long end, int advice, unsigned long *vm_flags)
 114 {
 115         return 0;
 116 }
 117
 118 static inline struct page *ksm_might_need_to_copy(struct page *page,
 119                         struct vm_area_struct *vma, unsigned long address)
 120 {
 121         return page;
 122 }
 123
 124 static inline int page_referenced_ksm(struct page *page,
 125                         struct mem_cgroup *memcg, unsigned long *vm_flags)
 126 {
 127         return 0;
 128 }
 129
 130 static inline int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
 131 {
 132         return 0;
 133 }
 134
 135 static inline int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page*,
 136                 struct vm_area_struct *, unsigned long, void *), void *arg)
 137 {
 138         return 0;
 139 }
 140
 141 static inline void ksm_migrate_page(struct page *newpage, struct page *oldpage)
 142 {
 143 }
 144 #endif /* CONFIG_MMU */
 145 #endif /* !CONFIG_KSM */
 146
 147 #endif /* __LINUX_KSM_H */