[PATCH] give swapper_space a set_page_dirty a_op

Give swapper_space a ->set_page_dirty() address_space_operation.

So swapcache pages do not need special-casing in
set_page_dirty_buffers().

mm/page-writeback.c

@@ -497,7 +497,7 @@ int __set_page_dirty_buffers(struct page *page)
 
 	spin_lock(&mapping->private_lock);
 
-	if (page_has_buffers(page) && !PageSwapCache(page)) {
+	if (page_has_buffers(page)) {
 		struct buffer_head *head = page_buffers(page);
 		struct buffer_head *bh = head;
 

mm/swap_state.c

@@ -51,6 +51,7 @@ static struct address_space_operations swap_aops = {
 	vm_writeback:	swap_vm_writeback,
 	writepage:	swap_writepage,
 	sync_page:	block_sync_page,
+	set_page_dirty:	__set_page_dirty_nobuffers,
 };
 
 /*