Add ability to remove migration ptes.

1. Modify page_check_address to support matching on ptes with
   SWP_TYPE_MIGRATION

2. Add functions to scan the anon vma and replace SWAP_TYPE_MIGRATION
   ptes with regular ones.

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

Index: linux-2.6.17-rc1/include/linux/rmap.h
===================================================================
--- linux-2.6.17-rc1.orig/include/linux/rmap.h	2006-04-02 20:22:10.000000000 -0700
+++ linux-2.6.17-rc1/include/linux/rmap.h	2006-04-06 11:31:48.407380000 -0700
@@ -105,6 +105,11 @@ pte_t *page_check_address(struct page *,
  */
 unsigned long page_address_in_vma(struct page *, struct vm_area_struct *);
 
+/*
+ * Used by page migration to restore ptes of anonymous pages
+ */
+void remove_migration_ptes(struct page *page, struct page *newpage);
+
 #else	/* !CONFIG_MMU */
 
 #define anon_vma_init()		do {} while (0)
Index: linux-2.6.17-rc1/mm/rmap.c
===================================================================
--- linux-2.6.17-rc1.orig/mm/rmap.c	2006-04-06 11:09:14.617856000 -0700
+++ linux-2.6.17-rc1/mm/rmap.c	2006-04-06 21:50:43.608324000 -0700
@@ -323,6 +323,43 @@ pte_t *page_check_address(struct page *p
 	return NULL;
 }
 
+#ifdef CONFIG_MIGRATION
+/*
+ * Get rid of all migration entries and replace them by
+ * references to the indicated page.
+ *
+ * Must hold mmap_sem lock on at least one of the vmas containing
+ * the page so that the anon_vma cannot vanish.
+ */
+void enable_ptes(struct page *page, struct page *newpage)
+{
+	struct anon_vma *anon_vma;
+	struct vm_area_struct *vma;
+	spinlock_t ptl;
+
+	if (!PageAnon(newpage))
+		return;
+
+	anon_vma = page_lock_anon_vma(newpage);
+	BUG_ON(!anon_vma);
+
+	list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
+		spinlock_t ptl;
+		pte_t *pte;
+
+		pte = page_check_address(page, vma->vm_mm,
+			page_address_in_vma(newpage, vma), &ptl);
+
+		if (pte) {
+			__put_page(page);
+			get_page(newpage);
+			pte_enable(pte);
+			spin_unlock(ptl);
+		}
+	}
+	spin_unlock(&anon_vma->lock);
+}
+#endif
 /*
  * Subfunctions of page_referenced: page_referenced_one called
  * repeatedly from either page_referenced_anon or page_referenced_file.