[PATCH] mm: de-skew page refcounting

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / include / linux / mm.h

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 85854b867463484cf1cc1c7fe76ae5c4f5ca4201..9bbddf228cd9493336be6d05765e44e47ffabfa2 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -286,34 +286,28 @@ struct page {
  *
  * Also, many kernel routines increase the page count before a critical
  * routine so they can be sure the page doesn't go away from under them.
- *
- * Since 2.6.6 (approx), a free page has ->_count = -1.  This is so that we
- * can use atomic_add_negative(-1, page->_count) to detect when the page
- * becomes free and so that we can also use atomic_inc_and_test to atomically
- * detect when we just tried to grab a ref on a page which some other CPU has
- * already deemed to be freeable.
- *
- * NO code should make assumptions about this internal detail!  Use the provided
- * macros which retain the old rules: page_count(page) == 0 is a free page.
  */
 
 /*
  * Drop a ref, return true if the logical refcount fell to zero (the page has
  * no users)
  */
-#define put_page_testzero(p)                           \
-       ({                                              \
-               BUG_ON(page_count(p) == 0);             \
-               atomic_add_negative(-1, &(p)->_count);  \
-       })
+static inline int put_page_testzero(struct page *page)
+{
+       BUG_ON(atomic_read(&page->_count) == 0);
+       return atomic_dec_and_test(&page->_count);
+}
 
 /*
- * Grab a ref, return true if the page previously had a logical refcount of
- * zero.  ie: returns true if we just grabbed an already-deemed-to-be-free page
+ * Try to grab a ref unless the page has a refcount of zero, return false if
+ * that is the case.
  */
-#define get_page_testone(p)    atomic_inc_and_test(&(p)->_count)
+static inline int get_page_unless_zero(struct page *page)
+{
+       return atomic_inc_not_zero(&page->_count);
+}
 
-#define set_page_count(p,v)    atomic_set(&(p)->_count, (v) - 1)
+#define set_page_count(p,v)    atomic_set(&(p)->_count, (v))
 #define __put_page(p)          atomic_dec(&(p)->_count)
 
 extern void FASTCALL(__page_cache_release(struct page *));
@@ -322,7 +316,7 @@ static inline int page_count(struct page *page)
 {
        if (PageCompound(page))
                page = (struct page *)page_private(page);
-       return atomic_read(&page->_count) + 1;
+       return atomic_read(&page->_count);
 }
 
 static inline void get_page(struct page *page)
@@ -1051,5 +1045,11 @@ int shrink_slab(unsigned long scanned, gfp_t gfp_mask,
 void drop_pagecache(void);
 void drop_slab(void);
 
+#ifndef CONFIG_MMU
+#define randomize_va_space 0
+#else
+extern int randomize_va_space;
+#endif
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_MM_H */