2 files changed, 42 insertions, 5 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c95d96ebd5ad..8c149fa4491d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -267,17 +267,28 @@ static inline int get_page_unless_zero(struct page *page)
         return atomic_inc_not_zero(&page->_count);
 }
 
+static inline struct page *compound_head(struct page *page)
+{
+        /*
+         * We could avoid the PageCompound(page) check if
+         * we would not overload PageTail().
+         *
+         * This check has to be done in several performance critical
+         * paths of the slab etc. IMHO PageTail deserves its own flag.
+         */
+        if (unlikely(PageCompound(page) && PageTail(page)))
+                return page->first_page;
+        return page;
+}
+
 static inline int page_count(struct page *page)
 {
-        if (unlikely(PageCompound(page)))
-                page = (struct page *)page_private(page);
-        return atomic_read(&page->_count);
+        return atomic_read(&compound_head(page)->_count);
 }
 
 static inline void get_page(struct page *page)
 {
-        if (unlikely(PageCompound(page)))
-                page = (struct page *)page_private(page);
+        page = compound_head(page);
         VM_BUG_ON(atomic_read(&page->_count) == 0);
         atomic_inc(&page->_count);
 }
@@ -314,6 +325,18 @@ static inline compound_page_dtor *get_compound_page_dtor(struct page *page)
         return (compound_page_dtor *)page[1].lru.next;
 }
 
+static inline int compound_order(struct page *page)
+{
+        if (!PageCompound(page) || PageTail(page))
+                return 0;
+        return (unsigned long)page[1].lru.prev;
+}
+
+static inline void set_compound_order(struct page *page, unsigned long order)
+{
+        page[1].lru.prev = (void *)order;
+}
+
 /*
  * Multiple processes may "see" the same page. E.g. for untouched
  * mappings of /dev/null, all processes see the same page full of
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 96326594e55d..a1e143634946 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -94,6 +94,12 @@
 /* PG_owner_priv_1 users should have descriptive aliases */
 #define PG_checked              PG_owner_priv_1 /* Used by some filesystems */
 
+/*
+ * Marks tail portion of a compound page. We currently do not reclaim
+ * compound pages so we can reuse a flag only used for reclaim here.
+ */
+#define PG_tail                 PG_reclaim
+
 #if (BITS_PER_LONG > 32)
 /*
  * 64-bit-only flags build down from bit 31
@@ -241,6 +247,14 @@ static inline void SetPageUptodate(struct page *page)
 #define __SetPageCompound(page) __set_bit(PG_compound, &(page)->flags)
 #define __ClearPageCompound(page) __clear_bit(PG_compound, &(page)->flags)
 
+/*
+ * Note: PG_tail is an alias of another page flag. The result of PageTail()
+ * is only valid if PageCompound(page) is true.
+ */
+#define PageTail(page)  test_bit(PG_tail, &(page)->flags)
+#define __SetPageTail(page)     __set_bit(PG_tail, &(page)->flags)
+#define __ClearPageTail(page)   __clear_bit(PG_tail, &(page)->flags)
+
 #ifdef CONFIG_SWAP
 #define PageSwapCache(page)     test_bit(PG_swapcache, &(page)->flags)
 #define SetPageSwapCache(page)  set_bit(PG_swapcache, &(page)->flags)