[PATCH] page migration: fail if page is in a vma flagged VM_LOCKED

page migration currently simply retries a couple of times if try_to_unmap()
fails without inspecting the return code.

However, SWAP_FAIL indicates that the page is in a vma that has the
VM_LOCKED flag set (if ignore_refs ==1).  We can check for that return code
and avoid retrying the migration.

migrate_page_remove_references() now needs to return a reason why the
failure occured.  So switch migrate_page_remove_references to use -Exx
style error messages.
Signed-off-by: NChristoph Lameter <clameter@sgi.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

fs/buffer.c

@@ -3060,6 +3060,7 @@ int buffer_migrate_page(struct page *newpage, struct page *page)
 {
 	struct address_space *mapping = page->mapping;
 	struct buffer_head *bh, *head;
+	int rc;
 
 	if (!mapping)
 		return -EAGAIN;
@@ -3069,8 +3070,9 @@ int buffer_migrate_page(struct page *newpage, struct page *page)
 
 	head = page_buffers(page);
 
-	if (migrate_page_remove_references(newpage, page, 3))
-		return -EAGAIN;
+	rc = migrate_page_remove_references(newpage, page, 3);
+	if (rc)
+		return rc;
 
 	bh = head;
 	do {

mm/vmscan.c

@@ -700,7 +700,7 @@ int migrate_page_remove_references(struct page *newpage,
 	 * the page.
 	 */
 	if (!mapping || page_mapcount(page) + nr_refs != page_count(page))
-		return 1;
+		return -EAGAIN;
 
 	/*
 	 * Establish swap ptes for anonymous pages or destroy pte
@@ -721,13 +721,15 @@ int migrate_page_remove_references(struct page *newpage,
 	 * If the page was not migrated then the PageSwapCache bit
 	 * is still set and the operation may continue.
 	 */
-	try_to_unmap(page, 1);
+	if (try_to_unmap(page, 1) == SWAP_FAIL)
+		/* A vma has VM_LOCKED set -> Permanent failure */
+		return -EPERM;
 
 	/*
 	 * Give up if we were unable to remove all mappings.
 	 */
 	if (page_mapcount(page))
-		return 1;
+		return -EAGAIN;
 
 	write_lock_irq(&mapping->tree_lock);
 
@@ -738,7 +740,7 @@ int migrate_page_remove_references(struct page *newpage,
 	if (!page_mapping(page) || page_count(page) != nr_refs ||
 			*radix_pointer != page) {
 		write_unlock_irq(&mapping->tree_lock);
-		return 1;
+		return -EAGAIN;
 	}
 
 	/*
@@ -813,10 +815,14 @@ EXPORT_SYMBOL(migrate_page_copy);
  */
 int migrate_page(struct page *newpage, struct page *page)
 {
+	int rc;
+
 	BUG_ON(PageWriteback(page));	/* Writeback must be complete */
 
-	if (migrate_page_remove_references(newpage, page, 2))
-		return -EAGAIN;
+	rc = migrate_page_remove_references(newpage, page, 2);
+
+	if (rc)
+		return rc;
 
 	migrate_page_copy(newpage, page);