[RFC] 4/4 Migration Cache - use for direct migration

[Lee Schermerhorn <lee.schermerhorn@hp.com>]

Migration Cache "V8" 4/4

This patch hooks the migration cache up to direct page migration.
If a destination page exists, and the old page is not already in
a swap cache, we place it in the migration cache instead.

If direct migration is successful, the page will be removed by
remove_from_swap(), et al.  If migration is not successful after
4 or 5 passes, migrate_pages() drops back to swapping.  In this
case, we must move the page from the migration cache to the swap
cache.

Signed-off-by:  Lee Schermerhorn <lee.schermerhorn@hp.com>

Index: linux-2.6.16-rc3-mm1/mm/vmscan.c
===================================================================
--- linux-2.6.16-rc3-mm1.orig/mm/vmscan.c	2006-02-15 10:50:59.000000000 -0500
+++ linux-2.6.16-rc3-mm1/mm/vmscan.c	2006-02-15 10:51:09.000000000 -0500
@@ -911,7 +911,12 @@ redo:
 		 * preserved.
 		 */
 		if (PageAnon(page) && !PageSwapCache(page)) {
-			if (!add_to_swap(page, GFP_KERNEL)) {
+			if (!to) {
+				if (!add_to_swap(page, GFP_KERNEL)) {
+					rc = -ENOMEM;
+					goto unlock_page;
+				}
+			} else if (add_to_migration_cache(page, GFP_KERNEL)) {
 				rc = -ENOMEM;
 				goto unlock_page;
 			}
@@ -989,6 +994,12 @@ redo:
 			 */
 			unlock_page(newpage);
 			newpage = NULL;
+			if (page_is_migration(page)) {
+				if (!migration_move_to_swap(page)) {
+					rc = -ENOMEM;
+					goto unlock_page;
+				}
+			}
 			rc = swap_page(page);
 			goto next;
 		}


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