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/sched.h>
  13 #include <linux/vmstat.h>
  14
  15 struct mmu_gather;
  16
  17 #ifdef CONFIG_KSM
  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,
  22                 struct mmu_gather **tlbp, unsigned long end);
  23
  24 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
  25 {
  26         if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags))
  27                 return __ksm_enter(mm);
  28         return 0;
  29 }
  30
  31 /*
  32  * For KSM to handle OOM without deadlock when it's breaking COW in a
  33  * likely victim of the OOM killer, exit_mmap() has to serialize with
  34  * ksm_exit() after freeing mm's pages but before freeing its page tables.
  35  * That leaves a window in which KSM might refault pages which have just
  36  * been finally unmapped: guard against that with ksm_test_exit(), and
  37  * use it after getting mmap_sem in ksm.c, to check if mm is exiting.
  38  */
  39 static inline bool ksm_test_exit(struct mm_struct *mm)
  40 {
  41         return atomic_read(&mm->mm_users) == 0;
  42 }
  43
  44 static inline void ksm_exit(struct mm_struct *mm,
  45                             struct mmu_gather **tlbp, unsigned long end)
  46 {
  47         if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
  48                 __ksm_exit(mm, tlbp, end);
  49 }
  50
  51 /*
  52  * A KSM page is one of those write-protected "shared pages" or "merged pages"
  53  * which KSM maps into multiple mms, wherever identical anonymous page content
  54  * is found in VM_MERGEABLE vmas.  It's a PageAnon page, with NULL anon_vma.
  55  */
  56 static inline int PageKsm(struct page *page)
  57 {
  58         return ((unsigned long)page->mapping == PAGE_MAPPING_ANON);
  59 }
  60
  61 /*
  62  * But we have to avoid the checking which page_add_anon_rmap() performs.
  63  */
  64 static inline void page_add_ksm_rmap(struct page *page)
  65 {
  66         if (atomic_inc_and_test(&page->_mapcount)) {
  67                 page->mapping = (void *) PAGE_MAPPING_ANON;
  68                 __inc_zone_page_state(page, NR_ANON_PAGES);
  69         }
  70 }
  71 #else  /* !CONFIG_KSM */
  72
  73 static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
  74                 unsigned long end, int advice, unsigned long *vm_flags)
  75 {
  76         return 0;
  77 }
  78
  79 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
  80 {
  81         return 0;
  82 }
  83
  84 static inline bool ksm_test_exit(struct mm_struct *mm)
  85 {
  86         return 0;
  87 }
  88
  89 static inline void ksm_exit(struct mm_struct *mm,
  90                             struct mmu_gather **tlbp, unsigned long end)
  91 {
  92 }
  93
  94 static inline int PageKsm(struct page *page)
  95 {
  96         return 0;
  97 }
  98
  99 /* No stub required for page_add_ksm_rmap(page) */
 100 #endif /* !CONFIG_KSM */
 101
 102 #endif