ksm: share anon page without allocating

[net-next-2.6.git] / mm / rmap.c

diff --git a/mm/rmap.c b/mm/rmap.c
index ebdf582ef18571d0c07d91dc9ee1e684251372af..2e38e904832729f8a7d99af924bc92f85fedb072 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -204,7 +204,7 @@ struct anon_vma *page_lock_anon_vma(struct page *page)
        unsigned long anon_mapping;
 
        rcu_read_lock();
-       anon_mapping = (unsigned long) page->mapping;
+       anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
        if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
                goto out;
        if (!page_mapped(page))
@@ -666,7 +666,9 @@ static void __page_check_anon_rmap(struct page *page,
  * @address:   the user virtual address mapped
  *
  * The caller needs to hold the pte lock, and the page must be locked in
- * the anon_vma case: to serialize mapping,index checking after setting.
+ * the anon_vma case: to serialize mapping,index checking after setting,
+ * and to ensure that PageAnon is not being upgraded racily to PageKsm
+ * (but PageKsm is never downgraded to PageAnon).
  */
 void page_add_anon_rmap(struct page *page,
        struct vm_area_struct *vma, unsigned long address)