4 files changed, 22 insertions, 4 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0e266fe1b4c4..a17b147c61e7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -296,6 +296,24 @@ void put_pages_list(struct list_head *pages);
 void split_page(struct page *page, unsigned int order);
 
 /*
+ * Compound pages have a destructor function.  Provide a
+ * prototype for that function and accessor functions.
+ * These are _only_ valid on the head of a PG_compound page.
+ */
+typedef void compound_page_dtor(struct page *);
+
+static inline void set_compound_page_dtor(struct page *page,
+                                                compound_page_dtor *dtor)
+{
+        page[1].lru.next = (void *)dtor;
+}
+
+static inline compound_page_dtor *get_compound_page_dtor(struct page *page)
+{
+        return (compound_page_dtor *)page[1].lru.next;
+}
+
+/*
  * Multiple processes may "see" the same page. E.g. for untouched
  * mappings of /dev/null, all processes see the same page full of
  * zeroes, and text pages of executables and shared libraries have
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2911a364481e..0ccc7f230252 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -109,7 +109,7 @@ static int alloc_fresh_huge_page(void)
         if (nid == MAX_NUMNODES)
                 nid = first_node(node_online_map);
         if (page) {
-                page[1].lru.next = (void *)free_huge_page;      /* dtor */
+                set_compound_page_dtor(page, free_huge_page);
                 spin_lock(&hugetlb_lock);
                 nr_huge_pages++;
                 nr_huge_pages_node[page_to_nid(page)]++;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index dc8753bdd47e..d539f83c62b6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -230,7 +230,7 @@ static void prep_compound_page(struct page *page, unsigned long order)
         int i;
         int nr_pages = 1 << order;
 
-        page[1].lru.next = (void *)free_compound_page;  /* set dtor */
+        set_compound_page_dtor(page, free_compound_page);
         page[1].lru.prev = (void *)order;
         for (i = 0; i < nr_pages; i++) {
                 struct page *p = page + i;
diff --git a/mm/swap.c b/mm/swap.c
index d9a3770d8f3c..017e72ca9bbb 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -57,9 +57,9 @@ static void put_compound_page(struct page *page)
 {
         page = (struct page *)page_private(page);
         if (put_page_testzero(page)) {
-                void (*dtor)(struct page *page);
+                compound_page_dtor *dtor;
 
-                dtor = (void (*)(struct page *))page[1].lru.next;
+                dtor = get_compound_page_dtor(page);
                 (*dtor)(page);
         }
 }