[PATCH] mm: make compound page destructor handling explicit

Currently we we use the lru head link of the second page of a compound page
to hold its destructor.  This was ok when it was purely an internal
implmentation detail.  However, hugetlbfs overrides this destructor
violating the layering.  Abstract this out as explicit calls, also
introduce a type for the callback function allowing them to be type
checked.  For each callback we pre-declare the function, causing a type
error on definition rather than on use elsewhere.

[akpm@osdl.org: cleanups]
Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 4 insertions, 4 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2911a36..0ccc7f2 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 dc8753b..d539f83 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 d9a3770..017e72c 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);
 	}
 }