[zero] polish ShardedOptimV2 unittest (#385)

* place params on cpu after zero init context

* polish code

* bucketzed cpu gpu tensor transter

* find a bug in sharded optim unittest

* add offload unittest for ShardedOptimV2.

* polish code and make it more robust

colossalai/zero/sharded_model/sharded_model_v2.py

@@ -79,6 +79,10 @@ class ShardedModelV2(nn.Module):
         self.reducer = ReduceScatterBucketer(reduce_scatter_bucket_size_mb)
         self._require_backward_grad_sync: bool = True
 
+    @property
+    def cpu_offload(self):
+        return self._cpu_offload
+
     def forward(self, *args: Any, **kwargs: Any) -> torch.Tensor:
         args, kwargs = cast_float_arguments(cast_tensor_to_fp16, *args, **kwargs)
         outputs = self.module(*args, **kwargs)

colossalai/zero/sharded_optim/sharded_optim_v2.py

@@ -44,6 +44,10 @@ class ShardedOptimizerV2(ColossalaiOptimizer):
         super().__init__(optimizer)
         self.shard_strategy = shard_strategy
         self.model: ShardedModelV2 = sharded_model
+        if cpu_offload and not sharded_model.cpu_offload:
+            raise RuntimeError(
+                f"ShardedOptimizerV2 using cpu_offload, but the sharded_model used to initialize it dose not use cpu_offload"
+            )
         self.device = torch.cuda.current_device() if not cpu_offload else torch.device('cpu')
         self.optim_state: OptimState = OptimState.UNSCALED
         self.dp_process_group = dp_process_group or gpc.get_group(ParallelMode.DATA)

tests/test_zero_data_parallel/test_sharded_optim_v2.py

@@ -24,21 +24,13 @@ def run_step(model, optimizer, data, label, criterion, enable_autocast=False):
     model.train()
     optimizer.zero_grad()
     with torch.cuda.amp.autocast(enabled=enable_autocast):
+        if criterion:
             y = model(data)
             loss = criterion(y, label)
-    loss = loss.float()
-    if isinstance(model, ShardedModelV2):
-        optimizer.backward(loss)
         else:
-        loss.backward()
-    optimizer.step()
-
-
-def run_step_no_criterion(model, optimizer, data, label, enable_autocast=False):
-    model.train()
-    optimizer.zero_grad()
-    with torch.cuda.amp.autocast(enabled=enable_autocast):
             loss = model(data, label)
+
+    loss = loss.float()
     if isinstance(model, ShardedModelV2):
         optimizer.backward(loss)
     else:
@@ -46,7 +38,7 @@ def run_step_no_criterion(model, optimizer, data, label, enable_autocast=False):
     optimizer.step()
 
 
-def run_dist(rank, world_size, port):
+def run_dist(rank, world_size, port, cpu_offload):
     colossalai.launch(config=CONFIG, rank=rank, world_size=world_size, host='localhost', port=port, backend='nccl')
     test_models = ['repeated_computed_layers', 'resnet18', 'bert']
     for model_name in test_models:
@@ -54,33 +46,33 @@ def run_dist(rank, world_size, port):
         shard_strategy = TensorShardStrategy()
         model, train_dataloader, test_dataloader, optimizer, criterion = get_components_func()
         model = model(checkpoint=True).cuda()
-        zero_model = ShardedModelV2(copy.deepcopy(model), shard_strategy)
+        zero_model = ShardedModelV2(copy.deepcopy(model),
+                                    shard_strategy,
+                                    offload_config=dict(device='cpu') if cpu_offload else None)
         if dist.get_world_size() > 1:
             model = DDP(model)
         optim = Adam(model.parameters(), lr=1e-3)
         sharded_optim = ShardedOptimizerV2(Adam(zero_model.parameters(), lr=1e-3),
                                            zero_model,
                                            shard_strategy,
+                                           cpu_offload=cpu_offload,
                                            initial_scale=2**5)
         for i, (data, label) in enumerate(train_dataloader):
             if i > 2:
                 break
             data, label = data.cuda(), label.cuda()
-            if criterion is None:
-                run_step_no_criterion(model, optim, data, label, False)
-                run_step_no_criterion(zero_model, sharded_optim, data, label, False)
-            else:
             run_step(model, optim, data, label, criterion, False)
             run_step(zero_model, sharded_optim, data, label, criterion, False)
             check_sharded_params_padding(model, zero_model, loose=True)
 
 
 @pytest.mark.dist
-@pytest.mark.parametrize("world_size", [1, 2, 4])
-def test_sharded_optim_v2(world_size):
-    run_func = partial(run_dist, world_size=world_size, port=free_port())
+@pytest.mark.parametrize("world_size", [1, 2])
+@pytest.mark.parametrize("cpu_offload", [True, False])
+def test_sharded_optim_v2(world_size, cpu_offload):
+    run_func = partial(run_dist, world_size=world_size, port=free_port(), cpu_offload=cpu_offload)
     mp.spawn(run_func, nprocs=world_size)
 
 
 if __name__ == '__main__':
-    test_sharded_optim_v2(world_size=2)
+    test_sharded_optim_v2(world_size=2, cpu_offload=True)