- * Locking:
- * - the page->mapcount field is protected by the PG_maplock bit,
- * which nests within the mm->page_table_lock,
- * which nests within the page lock.
- * - because swapout locking is opposite to the locking order
- * in the page fault path, the swapout path uses trylocks
- * on the mm->page_table_lock
+ * Locking: see "Lock ordering" summary in filemap.c.
+ * In swapout, page_map_lock is held on entry to page_referenced and
+ * try_to_unmap, so they trylock for i_mmap_lock and page_table_lock.