diff -Naur linux-2.6.28/include/linux/swap.h linux-2.6.28-tmem/include/linux/swap.h
--- linux-2.6.28/include/linux/swap.h	2008-12-24 16:26:37.000000000 -0700
+++ linux-2.6.28-tmem/include/linux/swap.h	2009-01-05 16:57:43.000000000 -0700
@@ -149,9 +149,33 @@
 	unsigned int pages;
 	unsigned int max;
 	unsigned int inuse_pages;
+	unsigned long * preswap_map;
+	unsigned int preswap_pages;
 	int next;			/* next entry on swap list */
 };
 
+#ifdef CONFIG_PRESWAP
+/* in preswap.c */
+extern void preswap_shrink(unsigned long);  /* REMOVE ME AFTER REMOVE HACK */
+extern int preswap_test(struct swap_info_struct *, unsigned long);
+extern void preswap_init(unsigned);
+extern int preswap_put(struct page *);
+extern int preswap_get(struct page *);
+extern void preswap_flush(unsigned, unsigned long);
+extern void preswap_flush_area(unsigned);
+/* in swapfile.c */
+extern int try_to_unuse(unsigned int, unsigned int, unsigned long);
+#define preswap_malloc vmalloc
+#else
+#define preswap_test(_x,_y) (0)
+#define preswap_init(_x) do { } while(0)
+#define preswap_put(_x) (0)
+#define preswap_get(_x) (0)
+#define preswap_flush(_x,_y) do { } while(0)
+#define preswap_flush_area(_x) do { } while(0)
+#define preswap_malloc(_x) (0)
+#endif
+
 struct swap_list_t {
 	int head;	/* head of priority-ordered swapfile list */
 	int next;	/* swapfile to be used next */
diff -Naur linux-2.6.28/mm/swapfile.c linux-2.6.28-tmem/mm/swapfile.c
--- linux-2.6.28/mm/swapfile.c	2008-12-24 16:26:37.000000000 -0700
+++ linux-2.6.28-tmem/mm/swapfile.c	2009-01-05 17:06:46.000000000 -0700
@@ -33,7 +33,7 @@
 #include <asm/tlbflush.h>
 #include <linux/swapops.h>
 
-static DEFINE_SPINLOCK(swap_lock);
+DEFINE_SPINLOCK(swap_lock);
 static unsigned int nr_swapfiles;
 long total_swap_pages;
 static int swap_overflow;
@@ -44,7 +44,7 @@
 static const char Bad_offset[] = "Bad swap offset entry ";
 static const char Unused_offset[] = "Unused swap offset entry ";
 
-static struct swap_list_t swap_list = {-1, -1};
+struct swap_list_t swap_list = {-1, -1};
 
 static struct swap_info_struct swap_info[MAX_SWAPFILES];
 
@@ -286,6 +286,7 @@
 				swap_list.next = p - swap_info;
 			nr_swap_pages++;
 			p->inuse_pages--;
+			preswap_flush(p - swap_info, offset);
 		}
 	}
 	return count;
@@ -696,7 +697,7 @@
  * Recycle to start on reaching the end, returning 0 when empty.
  */
 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
-					unsigned int prev)
+					unsigned int prev, unsigned int preswap)
 {
 	unsigned int max = si->max;
 	unsigned int i = prev;
@@ -722,6 +723,10 @@
 			prev = 0;
 			i = 1;
 		}
+		if (preswap) {
+			if (preswap_test(si,i)) break;
+			else continue;
+		}
 		count = si->swap_map[i];
 		if (count && count != SWAP_MAP_BAD)
 			break;
@@ -733,8 +738,12 @@
  * We completely avoid races by reading each swap page in advance,
  * and then search for the process using it.  All the necessary
  * page table adjustments can then be made atomically.
+ *
+ * if the boolean preswap is true, only unuse pages_to_unuse pages;
+ * pages_to_unuse==0 means all pages
  */
-static int try_to_unuse(unsigned int type)
+int try_to_unuse(unsigned int type, unsigned int preswap,
+	unsigned long pages_to_unuse)
 {
 	struct swap_info_struct * si = &swap_info[type];
 	struct mm_struct *start_mm;
@@ -770,7 +779,7 @@
 	 * one pass through swap_map is enough, but not necessarily:
 	 * there are races when an instance of an entry might be missed.
 	 */
-	while ((i = find_next_to_unuse(si, i)) != 0) {
+	while ((i = find_next_to_unuse(si, i, preswap)) != 0) {
 		if (signal_pending(current)) {
 			retval = -EINTR;
 			break;
@@ -947,6 +956,8 @@
 		 * interactive performance.
 		 */
 		cond_resched();
+		if (preswap && pages_to_unuse && !--pages_to_unuse)
+			break;
 	}
 
 	mmput(start_mm);
@@ -1291,7 +1302,7 @@
 	spin_unlock(&swap_lock);
 
 	current->flags |= PF_SWAPOFF;
-	err = try_to_unuse(type);
+	err = try_to_unuse(type,0,0);
 	current->flags &= ~PF_SWAPOFF;
 
 	if (err) {
@@ -1340,9 +1351,12 @@
 	swap_map = p->swap_map;
 	p->swap_map = NULL;
 	p->flags = 0;
+	preswap_flush_area(p - swap_info);
 	spin_unlock(&swap_lock);
 	mutex_unlock(&swapon_mutex);
 	vfree(swap_map);
+	if (p->preswap_map)
+		vfree(p->preswap_map);
 	inode = mapping->host;
 	if (S_ISBLK(inode->i_mode)) {
 		struct block_device *bdev = I_BDEV(inode);
@@ -1657,6 +1671,11 @@
 
 		error = 0;
 		memset(swap_map, 0, maxpages * sizeof(short));
+
+		p->preswap_map = preswap_malloc(maxpages / sizeof(long));
+		if (p->preswap_map)
+			memset(p->preswap_map, 0, maxpages / sizeof(long));
+
 		for (i = 0; i < swap_header->info.nr_badpages; i++) {
 			int page_nr = swap_header->info.badpages[i];
 			if (page_nr <= 0 || page_nr >= swap_header->info.last_page)
@@ -1719,6 +1738,7 @@
 	} else {
 		swap_info[prev].next = p - swap_info;
 	}
+	preswap_init(p - swap_info);
 	spin_unlock(&swap_lock);
 	mutex_unlock(&swapon_mutex);
 	error = 0;
diff -Naur linux-2.6.28/mm/page_io.c linux-2.6.28-tmem/mm/page_io.c
--- linux-2.6.28/mm/page_io.c	2008-12-24 16:26:37.000000000 -0700
+++ linux-2.6.28-tmem/mm/page_io.c	2009-01-05 17:11:38.000000000 -0700
@@ -102,6 +102,12 @@
 		unlock_page(page);
 		goto out;
 	}
+	if (preswap_put(page) == 1) {
+		set_page_writeback(page);
+		unlock_page(page);
+		end_page_writeback(page);
+		goto out;
+	}
 	bio = get_swap_bio(GFP_NOIO, page_private(page), page,
 				end_swap_bio_write);
 	if (bio == NULL) {
@@ -127,6 +133,11 @@
 
 	BUG_ON(!PageLocked(page));
 	BUG_ON(PageUptodate(page));
+	if (preswap_get(page) == 1) {
+		SetPageUptodate(page);
+		unlock_page(page);
+		goto out;
+	}
 	bio = get_swap_bio(GFP_KERNEL, page_private(page), page,
 				end_swap_bio_read);
 	if (bio == NULL) {