find_lock_page does not need to recheck ->index because if the page
is in the right mapping then the index must be the same. Also, tree_lock
does not need to be retaken after the page is locked in order to test
->mapped has not changed.

Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c
@@ -566,26 +566,26 @@ struct page *find_lock_page(struct addre
 {
 	struct page *page;
 
-	read_lock_irq(&mapping->tree_lock);
 repeat:
+	read_lock_irq(&mapping->tree_lock);
 	page = radix_tree_lookup(&mapping->page_tree, offset);
 	if (page) {
 		page_cache_get(page);
 		if (TestSetPageLocked(page)) {
 			read_unlock_irq(&mapping->tree_lock);
 			__lock_page(page);
-			read_lock_irq(&mapping->tree_lock);
 
 			/* Has the page been truncated while we slept? */
-			if (unlikely(page->mapping != mapping ||
-				     page->index != offset)) {
+			if (unlikely(page->mapping != mapping)) {
 				unlock_page(page);
 				page_cache_release(page);
 				goto repeat;
 			}
+			goto out;
 		}
 	}
 	read_unlock_irq(&mapping->tree_lock);
+out:
 	return page;
 }