diff --git a/paddle/optimizer/adadelta_optimizer.cc b/paddle/optimizer/adadelta_optimizer.cc
index 8d5865cd20fd1e0a8f413e080ddd27197f68bd64..a6b079ce256d83a3cab49802bfb83ab5020b17ad 100644
--- a/paddle/optimizer/adadelta_optimizer.cc
+++ b/paddle/optimizer/adadelta_optimizer.cc
@@ -37,6 +37,7 @@ const char* AdadeltaOptimizer::SerializeState(int* state_len) {
   state.set_nesterov(epsilon_);
   state.set_momentum(rho_);
   state.set_decay(decay_);
+  // can be used when memory alignment to system
   *state_len += CalStateSize(parameter_,
                              accum_gradient_,
                              accum_delta_,