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