Add multi_tensor for momentum optimizer and clear_grads (#37564)

* add multi_tensor for momentum and clear_grads for optimizer

* fix bug for dygraph

* add unittest

* refine comment

* add param_group

* refine regularizaiton logic

* del clear_grads

* add clear_grads

* add dispensable check of None

* refine clear_grad

* fix build bug

* refine code by comment

* refine code

* add multi tensor check

* refine param_group update

* add multi tensor for static mode

* refine comments

* delete useless comma for momentum

* refine comment for momentum

* refine code by commment

paddle/fluid/pybind/op_function_common.cc

@@ -688,7 +688,7 @@ std::vector<std::shared_ptr<imperative::VarBase>> GetVarBaseListFromArgs(
     ssize_t arg_idx, bool dispensable) {
   PyObject* list = PyTuple_GET_ITEM(args, arg_idx);
 
-  if (list == nullptr) {
+  if (list == nullptr || list == Py_None) {
     if (!dispensable) {
       PADDLE_THROW(platform::errors::InvalidArgument(
           "%s(): argument '%s' (position %d) must be list of Tensor, but got "

paddle/fluid/pybind/op_function_generator.h

@@ -58,6 +58,8 @@ std::map<std::string, std::set<std::string>> op_ins_map = {
     {"multiclass_nms3", {"BBoxes", "Scores", "RoisNum"}},
     {"box_coder", {"PriorBox", "PriorBoxVar", "TargetBox"}},
     {"momentum", {"Param", "Grad", "Velocity", "LearningRate", "MasterParam"}},
+    {"merged_momentum",
+     {"Param", "Grad", "Velocity", "LearningRate", "MasterParam"}},
     {"sparse_momentum", {"Param", "Grad", "Velocity", "Index", "LearningRate"}},
     {"rnn", {"Input", "PreState", "WeightList", "SequenceLength"}},
     {"run_program", {"X", "Params"}},
@@ -113,6 +115,7 @@ std::map<std::string, std::set<std::string>> op_outs_map = {
     {"multiclass_nms3", {"Out", "NmsRoisNum"}},
     {"generate_proposals_v2", {"RpnRois", "RpnRoiProbs", "RpnRoisNum"}},
     {"momentum", {"ParamOut", "VelocityOut", "MasterParamOut"}},
+    {"merged_momentum", {"ParamOut", "VelocityOut", "MasterParamOut"}},
     {"sparse_momentum", {"ParamOut", "VelocityOut"}},
     {"rnn", {"DropoutState", "Reserve", "Out", "State"}},
     {"run_program", {"DOut"}},
@@ -153,6 +156,7 @@ std::map<std::string, std::set<std::string>> op_passing_outs_map = {
      {"out_sum_1", "out_sum_2", "out_sum_3", "out_num_accumulates",
       "out_old_num_accumulates", "out_num_updates"}},
     {"momentum", {"ParamOut", "VelocityOut", "MasterParamOut"}},
+    {"merged_momentum", {"ParamOut", "VelocityOut", "MasterParamOut"}},
     {"sparse_momentum", {"ParamOut", "VelocityOut"}},
     {"batch_norm", {"MeanOut", "VarianceOut"}},
     {"sync_batch_norm", {"MeanOut", "VarianceOut"}},

paddle/fluid/pybind/pybind.cc

@@ -579,6 +579,14 @@ PYBIND11_MODULE(core_noavx, m) {
 
   m.def("disable_signal_handler", &DisableSignalHandler);
 
+  m.def("clear_gradients",
+        [](std::vector<std::shared_ptr<imperative::VarBase>> param_list,
+           bool set_to_zero) {
+          for (auto param : param_list) {
+            param->ClearGradient(set_to_zero);
+          }
+        });
+
 #if defined(PADDLE_WITH_CUDA) || defined(PADDLE_WITH_HIP)
   m.def("cudnn_version", &platform::DnnVersion);
   m.def("gpu_memory_available", []() {

python/paddle/fluid/tests/unittests/test_momentum_op.py

@@ -21,6 +21,7 @@ from paddle.fluid.op import Operator
 from op_test import OpTest
 import paddle
 import paddle.fluid as fluid
+import numpy
 
 
 def calculate_momentum_by_numpy(param,
@@ -805,5 +806,189 @@ class TestMomentumV2Group(TestMomentumV2):
         adam.clear_gradients()
 
 
+class TestMultiTensorMomentumDygraph(unittest.TestCase):
+    def _momentum_optimize_dygraph(self,
+                                   place,
+                                   use_param_attr=False,
+                                   use_param_group=False,
+                                   use_amp=False,
+                                   use_multi_tensor=False):
+        paddle.disable_static()
+        paddle.seed(10)
+        paddle.set_device(place)
+        input = paddle.randn((5, 5))
+        weight_attr = paddle.ParamAttr(
+            learning_rate=0.5,
+            regularizer=paddle.regularizer.L2Decay(1.0),
+            trainable=True)
+        if use_param_attr:
+            model = paddle.nn.Linear(5, 5, weight_attr)
+        else:
+            model = paddle.nn.Linear(5, 5)
+        if not use_param_group:
+            optimizer = paddle.optimizer.Momentum(
+                parameters=model.parameters(),
+                use_multi_tensor=use_multi_tensor,
+                multi_precision=use_amp)
+        else:
+            optimizer = paddle.optimizer.Momentum(
+                parameters=[{
+                    'params': model.parameters(),
+                    'weight_decay': 0.001,
+                    'learning_rate': 0.1,
+                    'momentum': 0.99
+                }],
+                use_multi_tensor=use_multi_tensor,
+                multi_precision=use_amp)
+        for idx in range(5):
+            if place == 'gpu' and use_amp == True:
+                model = paddle.amp.decorate(models=model, level='O2')
+                scaler = paddle.amp.GradScaler(init_loss_scaling=1024)
+            if place == 'gpu' and use_amp == True:
+                with paddle.amp.auto_cast(level='O2'):
+                    output = model(input)
+                    loss = paddle.mean(output)
+                scaled = scaler.scale(loss)
+                scaled.backward()
+                scaler.step(optimizer)
+                optimizer.clear_grad(set_to_zero=False)
+            else:
+                output = model(input)
+                loss = paddle.mean(output)
+                # This can be any optimizer supported by dygraph.
+                loss.backward()
+                optimizer.step()
+                optimizer.clear_grad(set_to_zero=False)
+        return output, model.parameters()
+
+    def _get_places(self):
+        places = ['cpu']
+        if paddle.is_compiled_with_cuda():
+            places.append('gpu')
+        return places
+
+    def _check_with_place_amp(self, place, use_amp):
+        output1, params1 = self._momentum_optimize_dygraph(
+            place=place, use_amp=use_amp, use_multi_tensor=True)
+        output2, params2 = self._momentum_optimize_dygraph(
+            place=place, use_amp=use_amp, use_multi_tensor=False)
+        self.assertEqual(np.allclose(output1, output2, rtol=1e-05), True)
+        for idx in range(len(params1)):
+            self.assertEqual(
+                np.allclose(
+                    params1[idx], params2[idx], rtol=1e-05), True)
+
+    def _check_with_param_arrt(self, place, use_amp):
+        output1, params1 = self._momentum_optimize_dygraph(
+            place=place,
+            use_amp=use_amp,
+            use_param_attr=True,
+            use_multi_tensor=True)
+        output2, params2 = self._momentum_optimize_dygraph(
+            place=place,
+            use_amp=use_amp,
+            use_param_attr=True,
+            use_multi_tensor=False)
+        self.assertEqual(np.allclose(output1, output2, rtol=1e-05), True)
+        for idx in range(len(params1)):
+            self.assertEqual(
+                np.allclose(
+                    params1[idx], params2[idx], rtol=1e-05), True)
+
+    def _check_with_param_group(self, place, use_amp):
+        output1, params1 = self._momentum_optimize_dygraph(
+            place=place,
+            use_amp=use_amp,
+            use_param_group=True,
+            use_multi_tensor=True)
+        output2, params2 = self._momentum_optimize_dygraph(
+            place=place,
+            use_amp=use_amp,
+            use_param_group=True,
+            use_multi_tensor=False)
+        self.assertEqual(np.allclose(output1, output2, rtol=1e-05), True)
+        for idx in range(len(params1)):
+            self.assertEqual(
+                np.allclose(
+                    params1[idx], params2[idx], rtol=1e-05), True)
+
+    def test_main(self):
+        for place in self._get_places():
+            use_amp_list = [True, False]
+            for use_amp in use_amp_list:
+                self._check_with_place_amp(place, use_amp)
+                self._check_with_param_arrt(place, use_amp)
+                self._check_with_param_group(place, use_amp)
+
+
+class TestMultiTensorMomentumStatic(unittest.TestCase):
+    def _momentum_optimize_static(self,
+                                  place,
+                                  use_amp=False,
+                                  use_multi_tensor=False):
+        paddle.enable_static()
+        paddle.seed(10)
+        np.random.seed(10)
+        if place == 'cpu':
+            use_amp = False
+        exe = paddle.static.Executor(place=place)
+        train_program = paddle.static.Program()
+        startup_program = paddle.static.Program()
+        optimizer = paddle.optimizer.Momentum(
+            multi_precision=use_amp, use_multi_tensor=use_multi_tensor)
+        if use_amp:
+            optimizer = paddle.static.amp.decorate(
+                optimizer,
+                init_loss_scaling=128.0,
+                use_dynamic_loss_scaling=True,
+                use_pure_fp16=True,
+                use_fp16_guard=False)
+        with paddle.static.program_guard(train_program, startup_program):
+            if use_amp:
+                data = paddle.static.data(
+                    shape=[2, 2], name='X', dtype='float16')
+            else:
+                data = paddle.static.data(
+                    shape=[2, 2], name='X', dtype='float32')
+            hidden = paddle.static.nn.fc(x=data, size=10)
+            loss = paddle.fluid.layers.mean(hidden)
+            optimizer.minimize(loss)
+        exe.run(startup_program)
+        if use_amp:
+            optimizer.amp_init(place=place, scope=paddle.static.global_scope())
+            x = numpy.random.random(size=(2, 2)).astype('float16')
+        else:
+            x = numpy.random.random(size=(2, 2)).astype('float32')
+        out = []
+        for idx in range(5):
+            loss_data, = exe.run(train_program,
+                                 feed={"X": x},
+                                 fetch_list=[loss.name])
+            out.append(loss_data)
+        return out
+
+    def _get_places(self):
+        places = ['cpu']
+        if paddle.is_compiled_with_cuda():
+            places.append('gpu')
+        return places
+
+    def _check_with_place_amp(self, place, use_amp):
+        output1 = self._momentum_optimize_static(
+            place=place, use_amp=use_amp, use_multi_tensor=True)
+        output2 = self._momentum_optimize_static(
+            place=place, use_amp=use_amp, use_multi_tensor=False)
+        for idx in range(len(output1)):
+            self.assertEqual(
+                np.allclose(
+                    output1[idx], output2[idx], rtol=1e-05), True)
+
+    def test_main(self):
+        for place in self._get_places():
+            use_amp_list = [True, False]
+            for use_amp in use_amp_list:
+                self._check_with_place_amp(place, use_amp)
+
+
 if __name__ == "__main__":
     unittest.main()

python/paddle/optimizer/momentum.py

@@ -24,6 +24,7 @@ from ..fluid import layers
 import paddle.fluid as fluid
 from paddle.fluid.regularizer import L2DecayRegularizer
 from paddle import _C_ops
+import paddle
 
 __all__ = []
 
@@ -74,6 +75,7 @@ class Momentum(Optimizer):
         multi_precision (bool, optional): Whether to use multi-precision during weight updating. Default is false.
         rescale_grad (float, optional): Multiply the gradient with `rescale_grad` before updating. \
             Often choose to be ``1.0/batch_size``.
+        use_multi_tensor (bool, optional): Whether to use multi-tensor strategy to update all parameters at once . Default is false.
         name (str, optional): The default value is None. Normally there is no need for user
                 to set this property. For more information, please refer to
                 :ref:`api_guide_Name` .
@@ -129,6 +131,7 @@ class Momentum(Optimizer):
                  grad_clip=None,
                  multi_precision=False,
                  rescale_grad=1.0,
+                 use_multi_tensor=False,
                  name=None):
         if learning_rate is None:
             raise ValueError("learning_rate is not set")
@@ -170,17 +173,22 @@ class Momentum(Optimizer):
             'regularization_method': self._regularization_method,
             'regularization_coeff': self._regularization_coeff,
         }
-        '''
-        if framework.in_dygraph_mode():
-            self.helper = LayerHelper(self.__class__.__name__)
-            if isinstance(self._parameter_list[0], dict):
-                for parameters in self._param_groups:
-                    for p in parameters['params']:
-                        self._add_accumulator(self._velocity_acc_str, p)
-            else:
-                for p in parameters:
-                    self._add_accumulator(self._velocity_acc_str, p)
-        '''
+        self._use_multi_tensor = use_multi_tensor
+        if self._use_multi_tensor:
+            self._param_dict = {'FP32_LODTensor': [], 'FP16_LODTensor': []}
+            self._velocity_dict = {'FP32_LODTensor': [], 'FP16_LODTensor': []}
+            self._master_weight_dict = {
+                'FP32_LODTensor': None,
+                'FP16_LODTensor': []
+            }
+            self._regularization_method_dict = {
+                'FP32_LODTensor': [],
+                'FP16_LODTensor': []
+            }
+            self._regularization_coeff_dict = {
+                'FP32_LODTensor': [],
+                'FP16_LODTensor': []
+            }
 
     def _update_regularization(self, weight_decay):
         reg_method = ""
@@ -353,6 +361,156 @@ class Momentum(Optimizer):
 
         return momentum_op
 
+    def _multi_tensor_init(self, target_block, parameters):
+        """
+        All parameters used for optimizer (such as: parameters, master_weight, velocity_acc for momentum) calculations are grouped into a python list by data type (float16, float32).
+        This function will be overridden in the corresponding optimizer file.
+
+        Args:
+            target_block: the block in which the loss tensor is present
+            parameters: list of parameter tensors for the optimizer
+        """
+        self._create_accumulators(target_block, parameters)
+        for param in parameters:
+            velocity_acc = self._get_accumulator(self._velocity_acc_str, param)
+            regularization_method = self._regularization_method
+            regularization_coeff = self._regularization_coeff
+            if hasattr(param, 'regularizer'):
+                # we skip param's l2decay before, so fuse it with momentum here.
+                if isinstance(param.regularizer, L2DecayRegularizer):
+                    regularization_method = "l2_decay"
+                    regularization_coeff = param.regularizer._regularization_coeff
+                else:
+                    regularization_method = ""
+                    regularization_coeff = 0.0
+            if param.dtype == paddle.float32:
+                self._param_dict['FP32_LODTensor'].append(param)
+                self._velocity_dict['FP32_LODTensor'].append(velocity_acc)
+                # fp32 no master weight
+                self._regularization_method_dict['FP32_LODTensor'].append(
+                    regularization_method)
+                self._regularization_coeff_dict['FP32_LODTensor'].append(
+                    regularization_coeff)
+            elif param.dtype == paddle.float16:
+                self._param_dict['FP16_LODTensor'].append(param)
+                self._velocity_dict['FP16_LODTensor'].append(velocity_acc)
+                if self._multi_precision:
+                    self._master_weight_dict['FP16_LODTensor'].append(
+                        self._master_weights[param.name])
+                else:
+                    self._master_weight_dict['FP16_LODTensor'] = None
+                self._regularization_method_dict['FP16_LODTensor'].append(
+                    regularization_method)
+                self._regularization_coeff_dict['FP16_LODTensor'].append(
+                    regularization_coeff)
+            else:
+                raise ValueError(
+                    "Now multi_tensor_momentum only support fp32 and fp16 parameters and grad is LOD_TENSOR."
+                )
+
+    def _append_optimize_multi_tensor_op(self, target_block,
+                                         parameters_and_grads):
+        """ 
+        For Multi Tensor, append optimize merged_operator to block.
+        """
+        assert isinstance(target_block, framework.Block)
+
+        grad_dict = {'FP32_LODTensor': [], 'FP16_LODTensor': []}
+        lr_dict = {'FP32_LODTensor': [], 'FP16_LODTensor': []}
+
+        if isinstance(parameters_and_grads, list):
+            for param_and_grad in parameters_and_grads:
+                if param_and_grad[1] is None:
+                    continue
+                if param_and_grad[0].stop_gradient is False:
+                    if param_and_grad[
+                            0].dtype == paddle.float32 and param_and_grad[
+                                1].type == core.VarDesc.VarType.LOD_TENSOR:
+                        grad_dict['FP32_LODTensor'].append(param_and_grad[1])
+                        lr = self._create_param_lr(param_and_grad)
+                        lr_dict['FP32_LODTensor'].append(lr)
+                    elif param_and_grad[
+                            0].dtype == paddle.float16 and param_and_grad[
+                                1].type == core.VarDesc.VarType.LOD_TENSOR:
+                        grad_dict['FP16_LODTensor'].append(param_and_grad[1])
+                        lr = self._create_param_lr(param_and_grad)
+                        lr_dict['FP16_LODTensor'].append(lr)
+        else:
+            for param_and_grad in parameters_and_grads['params']:
+                if param_and_grad[1] is None:
+                    continue
+                if param_and_grad[0].stop_gradient is False:
+                    param_grad_dict = dict()
+                    param_grad_dict['params'] = param_and_grad
+                    param_grad_dict.update({
+                        k: v
+                        for k, v in parameters_and_grads.items()
+                        if k != 'params'
+                    })
+                    param_and_grad = self._update_param_group(param_grad_dict)
+                    if param_and_grad[
+                            0].dtype == paddle.float32 and param_and_grad[
+                                1].type == core.VarDesc.VarType.LOD_TENSOR:
+                        grad_dict['FP32_LODTensor'].append(param_and_grad[1])
+                        lr = self._create_param_lr(param_and_grad)
+                        lr_dict['FP32_LODTensor'].append(lr)
+                    elif param_and_grad[
+                            0].dtype == paddle.float16 and param_and_grad[
+                                1].type == core.VarDesc.VarType.LOD_TENSOR:
+                        grad_dict['FP16_LODTensor'].append(param_and_grad[1])
+                        lr = self._create_param_lr(param_and_grad)
+                        lr_dict['FP16_LODTensor'].append(lr)
+
+        multi_tensor_list = ['FP32_LODTensor', 'FP16_LODTensor']
+        for key in multi_tensor_list:
+            if len(self._param_dict[key]) > 0:
+                if key == 'FP32_LODTensor':
+                    self._multi_precision = False
+
+                if framework.in_dygraph_mode():
+                    _, _, _ = _C_ops.merged_momentum(
+                        self._param_dict[key], grad_dict[key],
+                        self._velocity_dict[key], lr_dict[key],
+                        self._master_weight_dict[key], self._param_dict[key],
+                        self._velocity_dict[key], self._master_weight_dict[key],
+                        'mu', self._momentum, 'use_nesterov',
+                        self._use_nesterov, 'regularization_method',
+                        self._regularization_method_dict[key],
+                        'regularization_coeff',
+                        self._regularization_coeff_dict[key], 'multi_precision',
+                        self._multi_precision)
+                else:
+                    inputs = {
+                        "Param": self._param_dict[key],
+                        "Grad": grad_dict[key],
+                        "Velocity": self._velocity_dict[key],
+                        "LearningRate": lr_dict[key],
+                    }
+                    outputs = {
+                        "ParamOut": self._param_dict[key],
+                        "VelocityOut": self._velocity_dict[key],
+                    }
+                    attrs = {
+                        "mu": self._momentum,
+                        "use_nesterov": self._use_nesterov,
+                        "regularization_method":
+                        self._regularization_method_dict[key],
+                        "regularization_coeff":
+                        self._regularization_coeff_dict[key],
+                    }
+                    if self._multi_precision:
+                        inputs["MasterParam"] = self._master_weight_dict[key]
+                        outputs["MasterParamOut"] = self._master_weight_dict[
+                            key]
+                        attrs["multi_precision"] = self._multi_precision
+                    target_block.append_op(
+                        type="merged_momentum",
+                        inputs=inputs,
+                        outputs=outputs,
+                        attrs=attrs,
+                        stop_gradient=True)
+        return None
+
     def _update_param_group(self, parameters):
         self._momentum = parameters.get('momentum',
                                         self._default_dict['momentum'])

python/paddle/optimizer/optimizer.py

@@ -217,6 +217,11 @@ class Optimizer(object):
         else:
             self._param_groups = self._parameter_list
 
+        # NOTE: Multi Tensor: Pass in all parameters and gradients to the op kernel of the Optimizer at one time for updating for dygraph mode.
+        # Optimizer support list: [ paddle.optimizer.Momentum ].
+        self._use_multi_tensor = None
+        self._param_dict = {'FP32_LODTensor': [], 'FP16_LODTensor': []}
+
         self._auxiliary_vars = {}
 
     def _set_auxiliary_var(self, key, val):
@@ -676,14 +681,49 @@ class Optimizer(object):
 
         start = len(target_block.ops)
         self.helper = LayerHelper(self.__class__.__name__)
-        params_grads_device_map = parameters_and_grads['params'] if isinstance(
-            parameters_and_grads, dict) else parameters_and_grads
-        self._update_param_device_map(params_grads_device_map, target_block)
-        if isinstance(parameters_and_grads, list):
-            self._create_accumulators(
-                target_block,
-                [p[0] for p in parameters_and_grads if not p[0].stop_gradient])
 
+        self._create_global_learning_rate()
+
+        # NOTE: Multi Tensor support [ Momentum ] for dygraph mode
+        if self._use_multi_tensor and self.__class__.__name__ in ['Momentum']:
+            if len(self._param_dict['FP32_LODTensor']) == 0 and len(
+                    self._param_dict['FP16_LODTensor']) == 0:
+                if isinstance(parameters_and_grads, list):
+                    self._multi_tensor_init(target_block, [
+                        p[0] for p in parameters_and_grads
+                        if not p[0].stop_gradient
+                    ])
+                else:
+                    self._update_param_group(parameters_and_grads)
+                    self._multi_tensor_init(target_block, [
+                        p[0] for p in parameters_and_grads['params']
+                        if not p[0].stop_gradient
+                    ])
+            if framework.in_dygraph_mode():
+                self._append_optimize_multi_tensor_op(target_block,
+                                                      parameters_and_grads)
+            else:
+                self._update_param_device_map(parameters_and_grads,
+                                              target_block)
+                # NOTE: Multi Tensor requires all parameters to be in the same device and program.
+                # param_grad_list = [p_0,g_0,p_1,g_1,....]
+                param_grad_list = []
+                for param_and_grad in parameters_and_grads:
+                    if not param_and_grad[0].stop_gradient and param_and_grad[
+                            1] is not None:
+                        param_grad_list.append(param_and_grad[0])
+                        param_grad_list.append(param_and_grad[1])
+                with param_grad_list[0].block.program._optimized_guard(
+                        param_grad_list), name_scope("optimizer"):
+                    device = self._get_device_for_param(param_grad_list[0].name)
+                    with device_guard(device):
+                        self._append_optimize_multi_tensor_op(
+                            target_block, parameters_and_grads)
+        else:
+            if isinstance(parameters_and_grads, list):
+                self._create_accumulators(target_block, [
+                    p[0] for p in parameters_and_grads if not p[0].stop_gradient
+                ])
             else:
                 params_acc_dict = parameters_and_grads.copy()
                 params_acc_dict['params'] = [
@@ -692,16 +732,14 @@ class Optimizer(object):
                 ]
                 self._create_accumulators(target_block, params_acc_dict)
 
-        self._create_global_learning_rate()
-
             if framework.in_dygraph_mode():
-
                 if isinstance(parameters_and_grads, list):
                     for param_and_grad in parameters_and_grads:
                         if param_and_grad[1] is None:
                             continue
                         if param_and_grad[0].stop_gradient is False:
-                        self._append_optimize_op(target_block, param_and_grad)
+                            self._append_optimize_op(target_block,
+                                                     param_and_grad)
                 else:
                     for param_and_grad in parameters_and_grads['params']:
                         if param_and_grad[1] is None:
@@ -714,16 +752,22 @@ class Optimizer(object):
                                 for k, v in parameters_and_grads.items()
                                 if k != 'params'
                             })
-                        self._append_optimize_op(target_block, param_grad_dict)
+                            self._append_optimize_op(target_block,
+                                                     param_grad_dict)
             else:
+                params_grads_device_map = parameters_and_grads[
+                    'params'] if isinstance(parameters_and_grads,
+                                            dict) else parameters_and_grads
+                self._update_param_device_map(params_grads_device_map,
+                                              target_block)
                 for param_and_grad in parameters_and_grads:
                     if param_and_grad[1] is None:
                         continue
                     with param_and_grad[0].block.program._optimized_guard(
                             param_and_grad), name_scope("optimizer"):
                         if param_and_grad[0].stop_gradient is False:
-                        device = self._get_device_for_param(param_and_grad[0]
-                                                            .name)
+                            device = self._get_device_for_param(param_and_grad[
+                                0].name)
                             with device_guard(device):
                                 optimize_op = self._append_optimize_op(
                                     target_block, param_and_grad)
@@ -1002,12 +1046,17 @@ class Optimizer(object):
         return no_grad_set
 
     @framework.dygraph_only
-    def clear_grad(self):
+    def clear_grad(self, set_to_zero=True):
         """
         Clear the gradients of all optimized parameters for model.
 
         If not, new gradient will accumulat on previous gradient.
 
+        There are two method to clear grad: set_to_zero or delete grad.
+        
+        Args:
+            set_to_zero (bool, optional): If set grads to zero or not, default is True.
+        
         Returns:
             None
         
@@ -1029,16 +1078,18 @@ class Optimizer(object):
                 adam.clear_grad()
 
         """
+        param_list = []
         if self._parameter_list is None or not isinstance(
                 self._parameter_list[0], dict):
             for p in self._parameter_list:
                 if not p.stop_gradient:
-                    p.clear_gradient()
+                    param_list.append(p)
         else:
             for param_group in self._param_groups:
                 for p in param_group['params']:
                     if not p.stop_gradient:
-                        p.clear_gradient()
+                        param_list.append(p)
+        core.clear_gradients(param_list, set_to_zero)
 
     @imperative_base.no_grad
     def minimize(self,
@@ -1210,3 +1261,23 @@ class Optimizer(object):
             different optimization options. Only used in child class.
         """
         pass
+
+    @framework.dygraph_only
+    def _multi_tensor_init(self, target_block, parameters):
+        """
+        All parameters used for optimizer (such as: parameters, master_weight, velocity_acc for momentum) calculations are grouped into a python list by data type (float16, float32).
+        This function will be overridden in the corresponding optimizer file.
+
+        Args:
+            target_block: the block in which the loss tensor is present
+            parameters: list of parameter tensors for the optimizer
+        """
+        pass
+
+    @framework.dygraph_only
+    def _append_optimize_multi_tensor_op(self, target_block,
+                                         parameters_and_grads):
+        """ 
+        For Multi Tensor, append optimize merged_operator to block.
+        """
+        pass