[zero] improve adaptability for not-shard parameters (#708)

* adapt post grad hooks for not-shard parameters
* adapt optimizer for not-shard parameters
* offload gradients for not-replicated parameters

colossalai/nn/layer/moe/utils.py

@@ -8,7 +8,7 @@ from .experts import FFNExperts, TPExperts
 class ForceFP32Parameter(torch.nn.Parameter):
 
     def half(self, memory_format=None):
-        return self
+        return self.data
 
 
 class NormalNoiseGenerator:

colossalai/nn/optimizer/cpu_adam.py

@@ -142,6 +142,7 @@ class CPUAdam(torch.optim.Optimizer):
                 beta1, beta2 = group['betas']
 
                 if target_device.type == 'cpu':
+                    assert p.data.numel() == p.grad.data.numel(), "parameter and gradient should have the same size"
                     assert state['exp_avg'].device.type == 'cpu', "exp_avg should stay on cpu"
                     assert state['exp_avg_sq'].device.type == 'cpu', "exp_avg should stay on cpu"
                     self.cpu_adam_op.adam_update(self.opt_id, state['step'], group['lr'], beta1, beta2, group['eps'],
@@ -151,8 +152,8 @@ class CPUAdam(torch.optim.Optimizer):
                     assert state['exp_avg'].device.type == 'cuda', "exp_avg should stay on cuda"
                     assert state['exp_avg_sq'].device.type == 'cuda', "exp_avg should stay on cuda"
 
-                    bias_correction1 = 1 - beta1 ** state['step']
-                    bias_correction2 = 1 - beta2 ** state['step']
+                    bias_correction1 = 1 - beta1**state['step']
+                    bias_correction2 = 1 - beta2**state['step']
 
                     # adam on cuda
                     self.torch_adam_update(p.data, p.grad.data, state['exp_avg'], state['exp_avg_sq'], group['lr'],

colossalai/zero/init_ctx/init_context.py

@@ -213,7 +213,7 @@ class ZeroInitContext(InsertPostInitMethodToModuleSubClasses):
         src_rank = gpc.get_ranks_in_group(ParallelMode.DATA)[0]
         for param in self.param_list:
             assert hasattr(param, 'colo_attr')
-            if not param.colo_attr.param_is_sharded and param.is_replicated:
+            if not param.colo_attr.param_is_sharded and param.colo_attr.is_replicated:
                 dist.broadcast(tensor=param.data, src=src_rank, group=self.dp_process_group)
             param.colo_attr.remove_torch_payload()
 
@@ -239,9 +239,6 @@ class ZeroInitContext(InsertPostInitMethodToModuleSubClasses):
 
             self.model_numel_tensor += param.numel()
 
-            # mark whether the param is replicated
-            param.is_replicated = self.is_replicated
-
             # convert parameters to half
             param_half = half_fn(param)
             param.data = param_half
@@ -261,6 +258,13 @@ class ZeroInitContext(InsertPostInitMethodToModuleSubClasses):
                 self.shard_strategy.shard([param.colo_attr.sharded_data_tensor], self.dp_process_group)
                 param.data = param.colo_attr.sharded_data_tensor.payload    # set param.data to payload
 
+            # mark whether the param is replicated
+            param.colo_attr.is_replicated = self.is_replicated
+
+            # mark whether the param should keep not sharded
+            # if True, the param is used as Zero stage 2
+            param.colo_attr.keep_not_shard = not self.shard_param
+
             self.param_list.append(param)
 
         # We must cast buffers

colossalai/zero/sharded_model/sharded_model_v2.py

@@ -123,7 +123,7 @@ class ShardedModelV2(nn.Module):
             ZeroHook(self.shard_strategy, self._memstats_collector, self._stateful_tensor_mgr, self.process_group)
         ]
         register_ophooks_recursively(self.module, self._ophook_list)
-        self.param_hook_mgr = BaseParamHookMgr(self.sharded_params)
+        self.param_hook_mgr = BaseParamHookMgr(list(self.module.parameters()))
         self.param_hook_mgr.register_backward_hooks(self._grad_post_backward_hook)
 
         self.fp32_reduce_scatter = fp32_reduce_scatter
@@ -177,8 +177,8 @@ class ShardedModelV2(nn.Module):
             self.logger.error(f'dump memort tracer collected infomation to a {filename}', ranks=[0])
             if gpc.get_global_rank() == 0:
                 with open(filename, 'w+') as f:
-                    f.write(f'cuda reserved {torch.cuda.memory_reserved(get_current_device())/1e9} GB\n')
-                    f.write(f'cuda max allocated {torch.cuda.max_memory_allocated(get_current_device())/1e9} GB\n')
+                    f.write(f'cuda reserved {torch.cuda.memory_reserved(get_current_device()) / 1e9} GB\n')
+                    f.write(f'cuda max allocated {torch.cuda.max_memory_allocated(get_current_device()) / 1e9} GB\n')
                     f.write('CUDA model data (GB)\n')
                     f.write(str(self._memstats_collector.model_data_list('cuda', 'GB')))
                     f.write('\n')
@@ -254,10 +254,6 @@ class ShardedModelV2(nn.Module):
                 torch.cuda.current_stream().synchronize()
         self.reducer.free()
 
-        # all reduce gradients for unsharded parameters
-        reduce_list = [p for p in self.unshard_params if p.is_replicated]
-        bucket_allreduce(reduce_list, self.process_group)
-
         # 3. shard tensors not dealed in the zero hook
         tensor_list = []
         for p in self.sharded_params:
@@ -279,15 +275,6 @@ class ShardedModelV2(nn.Module):
             if not self._require_backward_grad_sync:
                 continue
 
-            # move unsharded param grad to saved_grad
-            if not p.colo_attr.param_is_sharded:
-                if p.colo_attr.offload_grad:
-                    colo_model_data_move_to_cpu(p.grad)
-                if p.colo_attr.saved_grad.is_null():
-                    p.colo_attr.saved_grad.reset_payload(p.grad.data)
-                else:
-                    p.colo_attr.saved_grad.payload.add_(p.grad.data)
-
             p.grad = None
 
     @torch.no_grad()
@@ -316,6 +303,18 @@ class ShardedModelV2(nn.Module):
         assert not grad.requires_grad, 'ShardedModel only works with gradients that don\'t require gradients'
         if not self._require_backward_grad_sync:
             return
+
+        if param.colo_attr.is_replicated:
+            self._reduce_scatter_handler(param, grad)
+        else:
+            self._save_grad(param, grad)
+
+        # used to cheat Pytorch, since we can't return None
+        empty_grad = torch.empty_like(grad)
+        free_storage(empty_grad)
+        return empty_grad
+
+    def _reduce_scatter_handler(self, param: Parameter, grad: torch.Tensor) -> None:
         self.comm_stream.wait_stream(torch.cuda.current_stream())
         with torch.cuda.stream(self.comm_stream):
             new_grad = grad.clone()
@@ -334,9 +333,6 @@ class ShardedModelV2(nn.Module):
                 self._reduce_scatter_callback(param, new_grad)
             orig_grad_data.record_stream(self.comm_stream)
         torch.cuda.current_stream().wait_stream(self.comm_stream)
-        empty_grad = torch.empty_like(grad)
-        free_storage(empty_grad)
-        return empty_grad
 
     def _reduce_scatter_callback(self, param: Parameter, reduced_grad: torch.Tensor) -> None:
         assert isinstance(reduced_grad,
@@ -345,21 +341,35 @@ class ShardedModelV2(nn.Module):
         if self.gradient_postdivide_factor > 1:
             # Average grad by world_size for consistency with PyTorch DDP.
             reduced_grad.data.div_(self.gradient_postdivide_factor)
-        # FIXME(ver217): remove the below line when impl eviction policy
+        self._save_grad(param, reduced_grad)
+
+    # FIXME(ver217): refactor the below line when impl eviction policy
+    def _save_grad(self, param: Parameter, grad: torch.Tensor):
+        # move gradient to cpu
         if param.colo_attr.offload_grad:
-            colo_model_data_move_to_cpu(reduced_grad)
+            colo_model_data_move_to_cpu(grad)
+
         if self.reuse_fp16_shard:
+            # make parameters point to gradient
+
             assert param.colo_attr.saved_grad.is_null(
             ), 'Gradien accumulation is not supported when reuse_fp16_shard=True'
-            param.colo_attr.sharded_data_tensor.reset_payload(reduced_grad)
+
+            param.colo_attr.saved_grad.reset_payload(grad)
+            param.colo_attr.sharded_data_tensor.reset_payload(grad)    # release the memory of param
+
+            if param.colo_attr.is_replicated:
                 param.colo_attr.sharded_data_tensor.is_sharded = True
-            param.colo_attr.saved_grad.reset_payload(param.colo_attr.sharded_data_tensor.payload)
         else:
-            reduced_grad = cast_tensor_to_fp32(reduced_grad)
+
+            fp32_grad = cast_tensor_to_fp32(grad)
+
             if param.colo_attr.saved_grad.is_null():
-                param.colo_attr.saved_grad.reset_payload(reduced_grad)
+                param.colo_attr.saved_grad.reset_payload(fp32_grad)
             else:
-                param.colo_attr.saved_grad.payload.add_(reduced_grad.view_as(param.colo_attr.saved_grad.payload))
+                param.colo_attr.saved_grad.payload.add_(fp32_grad.view_as(param.colo_attr.saved_grad.payload))
+
+        # keep saved_grad in HOLD state
         param.colo_attr.saved_grad.trans_state(TensorState.HOLD)
 
     def state_dict(self, destination=None, prefix='', keep_vars=False) -> 'OrderedDict[str, torch.Tensor]':

colossalai/zero/sharded_optim/sharded_optim_v2.py

@@ -68,9 +68,6 @@ class ShardedOptimizerV2(ColossalaiOptimizer):
         backoff_factor (float, optional): backoff_factor used by DynamicGradScaler. Defaults to 0.5.
         growth_interval (float, optional): growth_interval used by DynamicGradScaler. Defaults to 1000.
         hysteresis (float, optional): hysteresis used by DynamicGradScaler. Defaults to 2.
-        keep_unsharded (bool, optional): if True, optimizer won't shard unsharded parameters.
-            In Zero-2, set keep_unsharded to False.
-            In Zero-3, set keep_unsharded to True.
         max_scale (int, optional): max_scale used by DynamicGradScaler. Defaults to 2**32.
         dp_process_group (Optional[ProcessGroup], optional): data paralle process group. Defaults to None.
         mp_process_group (Optional[ProcessGroup], optional): model paralle process group. Defaults to None.
@@ -91,7 +88,6 @@ class ShardedOptimizerV2(ColossalaiOptimizer):
                  growth_interval: float = 1000,
                  hysteresis: float = 2,
                  max_scale: int = 2**32,
-                 keep_unsharded: bool = False,
                  dp_process_group: Optional[ProcessGroup] = None,
                  mp_process_group: Optional[ProcessGroup] = None) -> None:
         assert isinstance(sharded_model, ShardedModelV2), 'model must be wrapped with ShardedModel'
@@ -125,10 +121,6 @@ class ShardedOptimizerV2(ColossalaiOptimizer):
         self._found_overflow: Tensor = torch.FloatTensor([0]).to(torch.cuda.current_device())
         self._logger = get_dist_logger("ShardedOptimizerV2")
 
-        assert not (keep_unsharded and self._should_move_fp32_shards_h2d), \
-            "Keeping unsharded parameters can't be used with hybrid OS placement right now."
-        self.keep_unshard = keep_unsharded
-
         # Store fp32 param shards
         self._register_master_weight()
 
@@ -139,6 +131,10 @@ class ShardedOptimizerV2(ColossalaiOptimizer):
         if self._use_memory_tracer:
             GLOBAL_MODEL_DATA_TRACER.register_optimizer(self)
 
+    @property
+    def loss_scale(self):
+        return self.grad_scaler.scale.item()
+
     def get_memory_usage(self) -> Tuple[int, int]:
         """ Get the memory usage of the optimizer. Including master_params (param fp32),
         momentum (``self.state[p]['exp_avg']``) variance (``self.state[p]['exp_avg_sq']``)
@@ -166,6 +162,22 @@ class ShardedOptimizerV2(ColossalaiOptimizer):
 
         return cuda_use, cpu_use
 
+    def zero_grad(self, *args, **kwargs):
+        self._zero_grad()
+
+    def backward(self, loss: Tensor) -> None:
+        loss = self.loss_scale * loss
+        self.optim_state = OptimState.SCALED
+        self.model.backward(loss)
+
+    def backward_by_grad(self, tensor: Tensor, grad: Tensor) -> None:
+        self.model.backward_by_grad(tensor, grad)
+
+    def clip_grad_norm(self, model: nn.Module, max_norm: float):
+        if self.optim_state == OptimState.SCALED:
+            self._unscale_grads()
+        return super().clip_grad_norm(model, max_norm)
+
     def step(self, *args, **kwargs):
         self._prepare_grads()
         self._maybe_move_fp32_shards()
@@ -193,26 +205,9 @@ class ShardedOptimizerV2(ColossalaiOptimizer):
         self._logger.debug(
             f"After step ShardedOptimizerV2 consumes {self.get_memory_usage()[0] / 1e6} MB CUDA Memory, {self.get_memory_usage()[1] / 1e6} MB CUDA Memory!",
             ranks=[0])
-        self._copy_master_param_to_param_fp16()
+        self._copy_master_model_to_model_fp16()
         return ret
 
-    def backward(self, loss: Tensor) -> None:
-        loss = self.loss_scale * loss
-        self.optim_state = OptimState.SCALED
-        self.model.backward(loss)
-
-    def backward_by_grad(self, tensor: Tensor, grad: Tensor) -> None:
-        self.model.backward_by_grad(tensor, grad)
-
-    def clip_grad_norm(self, model: nn.Module, max_norm: float):
-        if self.optim_state == OptimState.SCALED:
-            self._unscale_grads()
-        return super().clip_grad_norm(model, max_norm)
-
-    @property
-    def loss_scale(self):
-        return self.grad_scaler.scale.item()
-
     def _check_overflow(self):
         # clear previous overflow record
         self._found_overflow.fill_(0.0)
@@ -240,9 +235,6 @@ class ShardedOptimizerV2(ColossalaiOptimizer):
                     p.grad.data.div_(self.loss_scale)
         self.optim_state = OptimState.UNSCALED
 
-    def zero_grad(self, *args, **kwargs):
-        self._zero_grad()
-
     def _zero_grad(self, recover_data: bool = False):
         """zero grad and maybe recover fp16 params
         When `reuse_fp16_shard` is enabled,
@@ -262,13 +254,11 @@ class ShardedOptimizerV2(ColossalaiOptimizer):
                 # p.colo_attr.sharded_data_tensor stores grad now
                 # we have to recover fp16 param
                 reuse_fp16_shard = p.colo_attr.saved_grad.data_ptr() == p.colo_attr.sharded_data_tensor.data_ptr()
-                p.colo_attr.saved_grad.set_null()
                 if recover_data and reuse_fp16_shard:
-                    # We should write like this to trigger ForceFP32Paramter's half method
-                    p.data = self.master_params[p].payload
-                    p.colo_attr.sharded_data_tensor.reset_payload(
-                        colo_model_tensor_clone(p.half(), torch.cuda.current_device()))
-                    p.colo_attr.remove_torch_payload()
+                    self._copy_master_param_to_param_fp16(p)
+                else:
+                    # release saved gradient
+                    p.colo_attr.saved_grad.set_null()
 
     def sync_grad(self):
         pass
@@ -278,14 +268,13 @@ class ShardedOptimizerV2(ColossalaiOptimizer):
         for group in self.optim.param_groups:
             for p in group['params']:
                 assert hasattr(p, 'colo_attr'), 'The parameter must be wrapped with ShardedParam'
-                is_param_sharded = p.colo_attr.sharded_data_tensor.is_sharded
-                if not is_param_sharded and not self.keep_unshard:
-                    # Please use keep_unsharded to control whether shard unsharded paramters
-                    # As we only store param shard, we shard it here
+                shard_flag = not p.colo_attr.sharded_data_tensor.is_sharded and p.colo_attr.is_replicated
+                if shard_flag:
+                    # we always shard replicated paramters
                     self.shard_strategy.shard([p.colo_attr.sharded_data_tensor], self.dp_process_group)
                 self.master_params[p] = StatefulTensor(
                     cast_tensor_to_fp32(p.colo_attr.sharded_data_tensor.payload.to(self.device)))
-                if not is_param_sharded and not self.keep_unshard:
+                if shard_flag:
                     # In this branch, there's no need to shard param
                     # So we gather here
                     self.shard_strategy.gather([p.colo_attr.sharded_data_tensor], self.dp_process_group)
@@ -328,31 +317,27 @@ class ShardedOptimizerV2(ColossalaiOptimizer):
                 # Now p.data is sharded
                 # So optimizer states are sharded naturally
 
-    def _copy_master_param_to_param_fp16(self):
+    def _copy_master_model_to_model_fp16(self):
         # Copy master param data (fp32) to payload of colo_attr (fp16)
         # TODO() improve efficiency by gathering tensors into a chunk and transfering
         # a chunk.
         for group in self.optim.param_groups:
             for p in group['params']:
-                is_param_sharded = p.colo_attr.sharded_data_tensor.is_sharded
-                if not is_param_sharded and not self.keep_unshard:
-                    # We use ZeRO-2 here
-                    # The `p.colo_attr.sharded_data_tensor` saves full fp16 param
-                    # But we only have updated fp32 param shard here
-                    # So we first shard full fp16 param and copy fp32 param shard to it
-                    # Then we will gather them
-                    self.shard_strategy.shard([p.colo_attr.sharded_data_tensor], self.dp_process_group)
-                # We have to use `copy_payload` instead of `reset_payload`
-                # Since p.data is fp32 and p.colo_attr.sharded_data_tensor is fp16
+                self._copy_master_param_to_param_fp16(p)
+
+    def _copy_master_param_to_param_fp16(self, p):
+        # flush gradient
+        p.colo_attr.saved_grad.set_null()
 
         # TODO() optimize this line CPU (fp32) -> GPU (fp16)
+        p.data = self.master_params[p].payload
         p.colo_attr.sharded_data_tensor.reset_payload(
             colo_model_tensor_clone(p.half(), p.colo_attr.sharded_data_tensor.device))
         p.colo_attr.remove_torch_payload()
 
-                if not is_param_sharded and not self.keep_unshard:
+        if p.colo_attr.keep_not_shard and p.colo_attr.is_replicated:
             # We gather full fp16 param here
+            p.colo_attr.sharded_data_tensor.is_sharded = True    # since only gradient is sharded, we should set to True
             self.shard_strategy.gather([p.colo_attr.sharded_data_tensor], self.dp_process_group)
 
         self.master_params[p].trans_state(TensorState.HOLD)
-                p.colo_attr.saved_grad.set_null()

tests/test_moe/test_moe_zero_init.py

@@ -71,9 +71,9 @@ def run_moe_zero_init(init_device_type, shard_strategy_class):
 
         # the parameters in moe experts is not replicated
         if 'experts' in name:
-            assert not param.is_replicated
+            assert not param.colo_attr.is_replicated
         else:
-            assert param.is_replicated
+            assert param.colo_attr.is_replicated
 
         if param.colo_attr.param_is_sharded:
             assert param.colo_attr.sharded_data_tensor.payload.device.type == init_device.type, \

tests/test_moe/test_moe_zero_model.py

@@ -36,7 +36,7 @@ def run_model_test(enable_autocast, shard_strategy_class):
 
     # check whether parameters are identical in ddp
     for name, p in zero_model.named_parameters():
-        if not p.colo_attr.param_is_sharded and p.is_replicated:
+        if not p.colo_attr.param_is_sharded and p.colo_attr.is_replicated:
             assert_equal_in_group(p.colo_attr.sharded_data_tensor.payload)
 
     model = MoeModel().half()

tests/test_moe/test_moe_zero_optim.py

@@ -48,8 +48,13 @@ def _run_step(model, optimizer, data, label, criterion, grad_handler):
 
 @parameterize("cpu_offload", [True])
 @parameterize("use_cpuadam", [True])    # We do not use Hybrid Adam right now, since it has a little bug
+@parameterize("reuse_fp16_shard", [True, False])
 @parameterize("shard_strategy_class", [TensorShardStrategy, BucketTensorShardStrategy])
-def _run_test_sharded_optim_v2(cpu_offload, shard_strategy_class, use_cpuadam, gpu_margin_mem_ratio=0.0):
+def _run_test_sharded_optim_v2(cpu_offload,
+                               shard_strategy_class,
+                               use_cpuadam,
+                               reuse_fp16_shard,
+                               gpu_margin_mem_ratio=0.0):
     shard_strategy = shard_strategy_class()
     if use_cpuadam and cpu_offload is False:
         return
@@ -63,17 +68,15 @@ def _run_test_sharded_optim_v2(cpu_offload, shard_strategy_class, use_cpuadam, g
             shard_param=True):
         zero_model = MoeModel()
 
-    zero_model = ShardedModelV2(
-        zero_model,
+    zero_model = ShardedModelV2(zero_model,
                                 shard_strategy,
                                 offload_config=dict(device='cpu') if cpu_offload else None,
                                 use_memory_tracer=gpu_margin_mem_ratio > 0.0,
-        reuse_fp16_shard=use_cpuadam,
-    )
+                                reuse_fp16_shard=reuse_fp16_shard)
 
     # check whether parameters are identical in ddp
     for name, p in zero_model.named_parameters():
-        if not p.colo_attr.param_is_sharded and p.is_replicated:
+        if not p.colo_attr.param_is_sharded and p.colo_attr.is_replicated:
             assert_equal_in_group(p.colo_attr.sharded_data_tensor.payload.to(get_current_device()))
 
     model = MoeModel().half()
@@ -88,8 +91,7 @@ def _run_test_sharded_optim_v2(cpu_offload, shard_strategy_class, use_cpuadam, g
                                        sharded_optim,
                                        cpu_offload=cpu_offload,
                                        initial_scale=2**5,
-                                       gpu_margin_mem_ratio=gpu_margin_mem_ratio,
-                                       keep_unsharded=True)
+                                       gpu_margin_mem_ratio=gpu_margin_mem_ratio)
 
     amp_config = dict(opt_level='O2', keep_batchnorm_fp32=False)
     apex_model, apex_optimizer = convert_to_apex_amp(model, optim, amp_config)

tests/test_zero_data_parallel/common.py

@@ -93,7 +93,7 @@ def check_grads_padding(model, zero_model, loose=False):
     rank = dist.get_rank()
     for (name, p), (zero_name, zero_p) in zip(model.named_parameters(), zero_model.named_parameters()):
         # zero_grad = zero_p.grad.clone().to(p.device)
-        if zero_p.colo_attr.param_is_sharded:
+        if zero_p.colo_attr.is_replicated:
             zero_grad = zero_p.colo_attr.saved_grad.payload.clone().to(p.device)
             chunks = torch.flatten(p.grad).chunk(dist.get_world_size())
             if rank >= len(chunks):
@@ -102,8 +102,9 @@ def check_grads_padding(model, zero_model, loose=False):
             if zero_grad.size(0) > grad.size(0):
                 zero_grad = zero_grad[:grad.size(0)]
         else:
-            grad = p.grad
             zero_grad = zero_p.colo_attr.saved_grad.payload
+            grad = p.grad.to(zero_grad.dtype)
+
         assert grad.dtype == zero_grad.dtype
         assert allclose(grad, zero_grad, loose=loose), f'diff: {grad - zero_grad}'
 
@@ -134,7 +135,7 @@ def check_sharded_model_params(model, zero_model, loose=False, reuse_fp16_shard=
             if zero_p.size(0) > p.size(0):
                 zero_p = zero_p[:p.size(0)]
         else:
-            zero_p = zero_p.colo_attr.sharded_data_tensor.payload
+            zero_p = zero_p.colo_attr.sharded_data_tensor.payload.to(p.device)
 
         assert p.dtype == zero_p.dtype
         assert allclose(p, zero_p, loose=loose), f'{p} vs {zero_p}'