diff --git a/paddle/fluid/imperative/layer.cc b/paddle/fluid/imperative/layer.cc
index 2176ac78bb6c9f3cf877dd9f66cf558e6f87711d..612503768079472ba233ee3fcd43a47fdba9a0cc 100644
--- a/paddle/fluid/imperative/layer.cc
+++ b/paddle/fluid/imperative/layer.cc
@@ -75,16 +75,6 @@ class Autograd {
   }
 
  private:
-  void AccumGrads(int grad_idx, Variable* grad,
-                  std::vector<Variable*>* op_grads) {
-    if (!(*op_grads)[grad_idx]) {
-      // FIXME(panyx0718): This should be a deep copy.
-      (*op_grads)[grad_idx] = grad;
-      return;
-    }
-    AddTo(grad, (*op_grads)[grad_idx]);
-  }
-
   std::map<OpBase*, int> ComputeDepCounts(OpBase* op) {
     std::map<OpBase*, int> ret;
 
@@ -108,14 +98,6 @@ class Autograd {
     return ret;
   }
 
-  std::vector<Variable*> CreateOpGrads(size_t count) {
-    std::vector<Variable*> op_grads;
-    for (size_t i = 0; i < count; ++i) {
-      op_grads.push_back(nullptr);
-    }
-    return op_grads;
-  }
-
   framework::Scope* scope_;
 };
 
@@ -133,7 +115,7 @@ framework::Variable* CreateVariable(const std::string& name,
     varname = string::Sprintf("%s@%d", varname, id);
   }
 
-  LOG(ERROR) << "creating var " << varname;
+  VLOG(3) << "creating var " << varname;
   framework::Variable* var = scope->Var(varname);
   framework::LoDTensor* tensor = var->GetMutable<framework::LoDTensor>();
 
@@ -165,22 +147,25 @@ std::vector<Variable*> OpBase::ApplyGrad(framework::Scope* scope) {
 
   for (const std::string& grad_invar : grad_op_desc_->InputArgumentNames()) {
     if (grad_to_var_->find(grad_invar) == grad_to_var_->end()) {
+      // grad op inputs can be forward inputs, so not in grad_to_var.
       continue;
     }
-    LOG(ERROR) << "op grad in var " << grad_invar;
+    VLOG(3) << "op grad in var " << grad_invar;
     block_->FindRecursiveOrCreateVar(grad_invar);
     framework::Variable* var = scope->Var(grad_invar);
     const std::string& invar = grad_to_var_->at(grad_invar);
     for (VarBase* varbase : *output_vars_) {
+      // Use the accumulated grads_ by sharing the input with grads_.
       if (varbase->var_desc_->Name() == invar) {
         var->GetMutable<framework::LoDTensor>()->ShareDataWith(
             varbase->grads_->Get<framework::LoDTensor>());
+        break;
       }
     }
   }
 
   for (const std::string& outvar : grad_op_desc_->OutputArgumentNames()) {
-    LOG(ERROR) << "grad outvar " << outvar;
+    VLOG(3) << "grad outvar " << outvar;
     block_->FindRecursiveOrCreateVar(outvar);
     framework::Variable* var = scope->Var(outvar);
     if (!var->IsInitialized()) {
@@ -199,6 +184,7 @@ std::vector<Variable*> OpBase::ApplyGrad(framework::Scope* scope) {
 
   opbase->Run(*scope, platform::CPUPlace());
 
+  // `ret` matches exactly with `input_vars_` of forward op.
   std::vector<Variable*> ret;
   for (size_t i = 0; i < input_vars_->size(); ++i) {
     bool found = false;
@@ -207,7 +193,7 @@ std::vector<Variable*> OpBase::ApplyGrad(framework::Scope* scope) {
       VarBase* origin_var = (*input_vars_)[i];
       std::string orig_var = grad_to_var_->at(outvar);
       PADDLE_ENFORCE(origin_var->var_desc_->Name() == orig_var);
-      LOG(ERROR) << "apply grad " << outvar << " with origin " << orig_var;
+      VLOG(3) << "apply grad " << outvar << " with origin " << orig_var;
       origin_var->ApplyGrad(scope, var);
       found = true;
       ret.push_back(var);
diff --git a/paddle/fluid/imperative/layer.h b/paddle/fluid/imperative/layer.h
index 0cf0c27a6a9b9f9fc78dfc331977f9ac20e87cb9..85a71ca83d21ed2595ddbe684300a46c05fed3af 100644
--- a/paddle/fluid/imperative/layer.h
+++ b/paddle/fluid/imperative/layer.h
@@ -36,10 +36,7 @@ class VarBase {
         var_(nullptr),
         grads_(nullptr) {}
 
-  virtual ~VarBase() {
-    LOG(ERROR) << "deleting var";
-    LOG(ERROR) << "done deleting var";
-  }
+  virtual ~VarBase() {}
 
   void ApplyGrad(framework::Scope* scope, framework::Variable* grad);
 
diff --git a/paddle/fluid/imperative/tracer.h b/paddle/fluid/imperative/tracer.h
index ff87993ffcaf88790cbae80a850cc8b8aabd1347..433d07c0e5aa0986ab1e9fe349ef865d2851c0c0 100644
--- a/paddle/fluid/imperative/tracer.h
+++ b/paddle/fluid/imperative/tracer.h
@@ -55,7 +55,7 @@ class Tracer {
              framework::BlockDesc* block) {
     framework::Scope* scope = GetScope(block);
     framework::OpDesc* op_desc = op->op_desc_;
-    LOG(ERROR) << "tracer tracing " << op_desc->Type();
+    VLOG(3) << "tracer tracing " << op_desc->Type();
     op_desc->InferShape(*block);
     op_desc->InferVarType(block);
     std::unique_ptr<framework::OperatorBase> op_base =
diff --git a/tools/print_signatures.py b/tools/print_signatures.py
index e2805c4e7e6aa26a5865b64a874feef672bf9b36..90c6626ecd63a9efeb725d136b6177cb03fab51d 100644
--- a/tools/print_signatures.py
+++ b/tools/print_signatures.py
@@ -27,6 +27,8 @@ import pydoc
 
 member_dict = collections.OrderedDict()
 
+experimental_namespace = {"paddle.fluid.imperative"}
+
 
 def visit_member(parent_name, member):
     cur_name = ".".join([parent_name, member.__name__])
@@ -50,6 +52,8 @@ def visit_member(parent_name, member):
 
 
 def visit_all_module(mod):
+    if (mod.__name__ in experimental_namespace):
+        return
     for member_name in (
             name
             for name in (mod.__all__ if hasattr(mod, "__all__") else dir(mod))