Modify try_to_unmap to produce swap migration entries

If we are trying to unmap an entry and do not have an associated
swapcache entry but are doing migration then create a special
swap pte of type SWP_TYPE_MIGRATION pointing to the pfn.

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

Index: linux-2.6.17-rc1/mm/rmap.c
===================================================================
--- linux-2.6.17-rc1.orig/mm/rmap.c	2006-04-06 10:47:24.000000000 -0700
+++ linux-2.6.17-rc1/mm/rmap.c	2006-04-06 11:09:14.000000000 -0700
@@ -595,14 +595,18 @@ static int try_to_unmap_one(struct page 
 	if (!pte)
 		goto out;
 
+	if (migration) {
+		ptep_disable(pte);
+		goto out_unmap;
+	}
+
 	/*
 	 * If the page is mlock()d, we cannot swap it out.
 	 * If it's recently referenced (perhaps page_referenced
 	 * skipped over this mm) then we should reactivate it.
 	 */
 	if ((vma->vm_flags & VM_LOCKED) ||
-			(ptep_clear_flush_young(vma, address, pte)
-				&& !migration)) {
+			(ptep_clear_flush_young(vma, address, pte))) {
 		ret = SWAP_FAIL;
 		goto out_unmap;
 	}
@@ -638,6 +642,7 @@ static int try_to_unmap_one(struct page 
 	} else
 		dec_mm_counter(mm, file_rss);
 
+finish:
 	page_remove_rmap(page);
 	page_cache_release(page);
 
Index: linux-2.6.17-rc1/mm/memory.c
===================================================================
--- linux-2.6.17-rc1.orig/mm/memory.c	2006-04-06 10:47:11.000000000 -0700
+++ linux-2.6.17-rc1/mm/memory.c	2006-04-06 11:29:16.000000000 -0700
@@ -2202,6 +2202,7 @@ static inline int handle_pte_fault(struc
 	pte_t entry;
 	pte_t old_entry;
 	spinlock_t *ptl;
+	struct page *page;
 
 	old_entry = entry = *pte;
 	if (!pte_present(entry)) {
@@ -2218,11 +2219,12 @@ static inline int handle_pte_fault(struc
 		return do_swap_page(mm, vma, address,
 					pte, pmd, write_access, entry);
 	}
-
 	ptl = pte_lockptr(mm, pmd);
 	spin_lock(ptl);
 	if (unlikely(!pte_same(*pte, entry)))
 		goto unlock;
+	if (unlikely(pte_disabled(entry)))
+		goto disabled_pte;
 	if (write_access) {
 		if (!pte_write(entry))
 			return do_wp_page(mm, vma, address,
@@ -2247,6 +2249,22 @@ static inline int handle_pte_fault(struc
 unlock:
 	pte_unmap_unlock(pte, ptl);
 	return VM_FAULT_MINOR;
+
+disabled_pte:
+	/*
+	 * Pte is valid but temporarily disabled.
+	 * This is typically done by page migration while
+	 * migrating a page. In order to reenable the pte
+	 * we need to get the page lock.
+	 */
+	page = vm_normal_page(vma, address, entry);
+	get_page(page);
+	pte_unmap_unlock(pte, ptl);
+	lock_page(page);
+	pte_enable(pte);
+	unlock_lock(page);
+	put_page(page);
+	return VM_FAULT_MINOR;
 }
 
 /*