private void unmap() throws IOException {
      try {
        unmapBuffer(pageBuffer);
      }
      catch (Throwable t) {
        if (FAIL_ON_FAILED_UNMAP) {
          throw new IOException("Can't unmap pageBuffer", t);
        }
        else {
          THROTTLED_LOG.warn("Can't unmap pageBuffer explicitly -- rely on GC to do it eventually", t);
        }
      }
    }
private void unmap()