code: @InService(PageServiceSync.class)
    public void afterDataFlush(Page newPage, int sequenceFlush)
    {
      Page page = _pages.get(newPage.getId());
      
      if (page == newPage) {
        page.afterDataFlush(this, sequenceFlush);
      }
      else {
        System.out.println("AfterDataFlush mismatch: " + page + " " + newPage);
      }
    }
docs: After the checkpoint is written to mmap/file, the stub is valid
  for reloading.