4 * Memory merging support.
6 * This code enables dynamic sharing of identical pages found in different
7 * memory areas, even if they are not shared by fork().
10 #include <linux/bitops.h>
12 #include <linux/sched.h>
13 #include <linux/vmstat.h>
18 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
19 unsigned long end, int advice, unsigned long *vm_flags);
20 int __ksm_enter(struct mm_struct *mm);
21 void __ksm_exit(struct mm_struct *mm);
23 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
25 if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags))
26 return __ksm_enter(mm);
31 * For KSM to handle OOM without deadlock when it's breaking COW in a
32 * likely victim of the OOM killer, exit_mmap() has to serialize with
33 * ksm_exit() after freeing mm's pages but before freeing its page tables.
34 * That leaves a window in which KSM might refault pages which have just
35 * been finally unmapped: guard against that with ksm_test_exit(), and
36 * use it after getting mmap_sem in ksm.c, to check if mm is exiting.
38 static inline bool ksm_test_exit(struct mm_struct *mm)
40 return atomic_read(&mm->mm_users) == 0;
43 static inline void ksm_exit(struct mm_struct *mm)
45 if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
50 * A KSM page is one of those write-protected "shared pages" or "merged pages"
51 * which KSM maps into multiple mms, wherever identical anonymous page content
52 * is found in VM_MERGEABLE vmas. It's a PageAnon page, with NULL anon_vma.
54 static inline int PageKsm(struct page *page)
56 return ((unsigned long)page->mapping == PAGE_MAPPING_ANON);
60 * But we have to avoid the checking which page_add_anon_rmap() performs.
62 static inline void page_add_ksm_rmap(struct page *page)
64 if (atomic_inc_and_test(&page->_mapcount)) {
65 page->mapping = (void *) PAGE_MAPPING_ANON;
66 __inc_zone_page_state(page, NR_ANON_PAGES);
69 #else /* !CONFIG_KSM */
71 static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
72 unsigned long end, int advice, unsigned long *vm_flags)
77 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
82 static inline bool ksm_test_exit(struct mm_struct *mm)
87 static inline void ksm_exit(struct mm_struct *mm)
91 static inline int PageKsm(struct page *page)
96 /* No stub required for page_add_ksm_rmap(page) */
97 #endif /* !CONFIG_KSM */