1 files changed, 29 insertions, 0 deletions

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index eb2a448981ee..a485c14ecd5d 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -10,6 +10,7 @@
 #include <linux/bitops.h>
 #include <linux/mm.h>
 #include <linux/sched.h>
+#include <linux/vmstat.h>
 
 #ifdef CONFIG_KSM
 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
@@ -29,6 +30,27 @@ static inline void ksm_exit(struct mm_struct *mm)
         if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
                 __ksm_exit(mm);
 }
+
+/*
+ * A KSM page is one of those write-protected "shared pages" or "merged pages"
+ * which KSM maps into multiple mms, wherever identical anonymous page content
+ * is found in VM_MERGEABLE vmas.  It's a PageAnon page, with NULL anon_vma.
+ */
+static inline int PageKsm(struct page *page)
+{
+        return ((unsigned long)page->mapping == PAGE_MAPPING_ANON);
+}
+
+/*
+ * But we have to avoid the checking which page_add_anon_rmap() performs.
+ */
+static inline void page_add_ksm_rmap(struct page *page)
+{
+        if (atomic_inc_and_test(&page->_mapcount)) {
+                page->mapping = (void *) PAGE_MAPPING_ANON;
+                __inc_zone_page_state(page, NR_ANON_PAGES);
+        }
+}
 #else  /* !CONFIG_KSM */
 
 static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
@@ -45,6 +67,13 @@ static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 static inline void ksm_exit(struct mm_struct *mm)
 {
 }
+
+static inline int PageKsm(struct page *page)
+{
+        return 0;
+}
+
+/* No stub required for page_add_ksm_rmap(page) */
 #endif /* !CONFIG_KSM */
 
 #endif