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-2.6.16-mm2/mm/rmap.c
===================================================================
--- linux-2.6.16-mm2.orig/mm/rmap.c	2006-03-31 09:24:04.000000000 -0800
+++ linux-2.6.16-mm2/mm/rmap.c	2006-03-31 09:25:12.000000000 -0800
@@ -620,6 +620,17 @@ static int try_to_unmap_one(struct page 
 
 	if (PageAnon(page)) {
 		swp_entry_t entry = { .val = page_private(page) };
+
+		if (!PageSwapCache(page) && migration) {
+			/*
+			 * Store the pfn of the page in a special migration
+			 * pte. do_swap_page() will wait until the page is unlocked
+			 * and then restart the fault handling.
+			 */
+			entry = swp_entry(SWP_TYPE_MIGRATION, page_to_pfn(page));
+			set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
+			goto finish;
+		}
 		/*
 		 * Store the swap location in the pte.
 		 * See handle_pte_fault() ...
@@ -638,6 +649,7 @@ static int try_to_unmap_one(struct page 
 	} else
 		dec_mm_counter(mm, file_rss);
 
+finish:
 	page_remove_rmap(page);
 	page_cache_release(page);