Add migration swap type

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.16-mm2/mm/swap_state.c
===================================================================
--- linux-2.6.16-mm2.orig/mm/swap_state.c	2006-03-30 21:21:06.000000000 -0800
+++ linux-2.6.16-mm2/mm/swap_state.c	2006-03-30 22:57:25.000000000 -0800
@@ -10,6 +10,7 @@
 #include <linux/mm.h>
 #include <linux/kernel_stat.h>
 #include <linux/swap.h>
+#include <linux/swapops.h>
 #include <linux/init.h>
 #include <linux/pagemap.h>
 #include <linux/buffer_head.h>
@@ -300,6 +301,13 @@ struct page * lookup_swap_cache(swp_entr
 {
 	struct page *page;
 
+	/*
+	 * If the swap type is SWP_TYPE_MIGRATION then the
+	 * swap entry contains the pfn of a page.
+	 */
+	if (swp_type(entry) == SWP_TYPE_MIGRATION)
+		return pfn_to_page(swp_offset(entry));
+
 	page = find_get_page(&swapper_space, entry.val);
 
 	if (page)
Index: linux-2.6.16-mm2/mm/swapfile.c
===================================================================
--- linux-2.6.16-mm2.orig/mm/swapfile.c	2006-03-30 21:21:06.000000000 -0800
+++ linux-2.6.16-mm2/mm/swapfile.c	2006-03-30 22:57:25.000000000 -0800
@@ -395,6 +395,9 @@ void free_swap_and_cache(swp_entry_t ent
 	struct swap_info_struct * p;
 	struct page *page = NULL;
 
+	if (swp_type(entry) == SWP_TYPE_MIGRATION)
+		return;
+
 	p = swap_info_get(entry);
 	if (p) {
 		if (swap_entry_free(p, swp_offset(entry)) == 1)
@@ -1704,6 +1707,9 @@ int swap_duplicate(swp_entry_t entry)
 	int result = 0;
 
 	type = swp_type(entry);
+	if (type == SWP_TYPE_MIGRATION)
+		return 1;
+
 	if (type >= nr_swapfiles)
 		goto bad_file;
 	p = type + swap_info;
Index: linux-2.6.16-mm2/include/linux/swap.h
===================================================================
--- linux-2.6.16-mm2.orig/include/linux/swap.h	2006-03-30 21:21:05.000000000 -0800
+++ linux-2.6.16-mm2/include/linux/swap.h	2006-03-30 22:57:25.000000000 -0800
@@ -29,7 +29,10 @@ static inline int current_is_kswapd(void
  * the type/offset into the pte as 5/27 as well.
  */
 #define MAX_SWAPFILES_SHIFT	5
-#define MAX_SWAPFILES		(1 << MAX_SWAPFILES_SHIFT)
+#define MAX_SWAPFILES		((1 << MAX_SWAPFILES_SHIFT)-1)
+
+/* Use last entry for page migration swap entries */
+#define SWP_TYPE_MIGRATION	MAX_SWAPFILES
 
 /*
  * Magic header for a swap area. The first part of the union is