[zero] add stateful tensor (#549)

colossalai/engine/ophooks/zero_hook.py

@@ -64,8 +64,8 @@ class ZeroHook(BaseOpHook):
             if param.grad is not None:
                 if param.col_attr.bwd_count == 0:
                     # We haven't stored local accumulated grad yet
-                    assert param.col_attr.fp32_grad is None
-                    param.col_attr.fp32_grad = param.grad.data
+                    assert param.col_attr.fp32_grad.is_null()
+                    param.col_attr.fp32_grad.reset_payload(param.grad.data)
                     param.grad = None
                 else:
                     # We have stored local accumulated grad

colossalai/zero/sharded_model/_utils.py

@@ -2,6 +2,8 @@ from typing import Any, Callable, List, Tuple
 
 import torch
 import torch.nn.functional as F
+from typing import Union
+from colossalai.zero.sharded_param.tensorful_state import StatefulTensor
 
 
 def get_gradient_predivide_factor(world_size: int) -> float:
@@ -30,12 +32,17 @@ def alloc_storage(data: torch.Tensor, size: torch.Size) -> None:
 
 
 def cast_tensor_to_fp16(tensor: torch.Tensor) -> torch.Tensor:
+    if isinstance(tensor, StatefulTensor):
+        tensor = tensor.payload
     if torch.is_floating_point(tensor) and tensor.dtype is torch.float32:
         return tensor.half()
     return tensor
 
 
-def cast_tensor_to_fp32(tensor: torch.Tensor) -> torch.Tensor:
+def cast_tensor_to_fp32(tensor: Union[torch.Tensor, StatefulTensor]) -> torch.Tensor:
+    if isinstance(tensor, StatefulTensor):
+        tensor = tensor.payload
+
     if torch.is_floating_point(tensor) and tensor.dtype is torch.float16:
         return tensor.float()
     return tensor

colossalai/zero/sharded_model/sharded_model_v2.py

@@ -25,6 +25,7 @@ from torch.nn.parameter import Parameter
 
 from ._utils import (cast_float_arguments, cast_tensor_to_fp16, cast_tensor_to_fp32, chunk_and_pad, free_storage,
                      get_gradient_predivide_factor)
+from colossalai.zero.sharded_param.tensorful_state import StatefulTensor
 
 
 class ShardedModelV2(nn.Module):
@@ -233,16 +234,17 @@ class ShardedModelV2(nn.Module):
             if self.reuse_fp16_shard:
                 grad_payload = p.col_attr.sharded_data_tensor.payload
             else:
-                grad_payload = cast_tensor_to_fp32(p.col_attr.fp16_grad)
+                grad_payload = cast_tensor_to_fp32(p.col_attr.fp16_grad.payload)
+            assert isinstance(grad_payload, torch.Tensor)
             if p.col_attr.offload_grad:
                 colo_model_data_move_to_cpu(grad_payload)
-            if p.col_attr.fp32_grad is not None:
+            if not p.col_attr.fp32_grad.is_null():
                 assert not self.reuse_fp16_shard, 'Gradien accumulation is not supported when reuse_fp16_shard=True'
-                p.col_attr.fp32_grad.add_(grad_payload.view_as(p.col_attr.fp32_grad))
-                grad_payload = p.col_attr.fp32_grad
+                p.col_attr.fp32_grad.payload.add_(grad_payload.view_as(p.col_attr.fp32_grad.payload))
+                grad_payload = p.col_attr.fp32_grad.payload
             p.grad.data = grad_payload
-            p.col_attr.fp16_grad = None
-            p.col_attr.fp32_grad = None
+            p.col_attr.fp16_grad.set_null()
+            p.col_attr.fp32_grad.set_null()
 
     @torch.no_grad()
     def _grad_post_backward_hook(self, param: Parameter, grad: torch.Tensor) -> Optional[torch.Tensor]:
@@ -293,6 +295,8 @@ class ShardedModelV2(nn.Module):
         return empty_grad
 
     def _reduce_scatter_callback(self, param: Parameter, reduced_grad: torch.Tensor) -> None:
+        assert isinstance(reduced_grad,
+                          torch.Tensor), f"_reduce_scatter_callback accept reduced_grad as {type(reduced_grad)}"
         reduced_grad = reduced_grad.view(-1)
         if self.gradient_postdivide_factor > 1:
             # Average grad by world_size for consistency with PyTorch DDP.
@@ -301,7 +305,7 @@ class ShardedModelV2(nn.Module):
             param.col_attr.sharded_data_tensor.reset_payload(reduced_grad.data)
             param.col_attr.sharded_data_tensor.is_sharded = True
         else:
-            param.col_attr.fp16_grad = reduced_grad.data
+            param.col_attr.fp16_grad = StatefulTensor(reduced_grad.data)
 
     def state_dict(self, destination=None, prefix='', keep_vars=False) -> 'OrderedDict[str, torch.Tensor]':
         self.shard_strategy.gather([p.col_attr.sharded_data_tensor for p in self.module.parameters()],

colossalai/zero/sharded_param/sharded_param.py

@@ -3,6 +3,7 @@ import torch.distributed as dist
 from colossalai.zero.sharded_param import ShardedTensor
 from typing import Optional, Tuple
 from colossalai.utils.memory_utils.utils import colo_tensor_mem_usage
+from .tensorful_state import StatefulTensor, TensorState
 
 
 class ShardedParamV2(object):
@@ -12,8 +13,8 @@ class ShardedParamV2(object):
                  process_group: Optional[dist.ProcessGroup] = None,
                  rm_torch_payload=False) -> None:
         self._sharded_data_tensor: ShardedTensor = ShardedTensor(param.data, process_group)
-        self.fp16_grad: Optional[torch.Tensor] = None
-        self.fp32_grad: Optional[torch.Tensor] = None
+        self.fp16_grad: StatefulTensor = StatefulTensor(None, TensorState.FREE)
+        self.fp32_grad: StatefulTensor = StatefulTensor(None, TensorState.FREE)
         # This attribute must be initialized in ShardedModel
         self.offload_grad: bool = False
 
@@ -64,12 +65,12 @@ class ShardedParamV2(object):
         _update_mem_use(self.sharded_data_tensor.payload)
         address_set.add(self.sharded_data_tensor.payload.data_ptr())
 
-        if self.fp16_grad is not None and self.fp16_grad.data_ptr() not in address_set:
-            _update_mem_use(self.fp16_grad)
+        if not self.fp16_grad.is_null() and self.fp16_grad.data_ptr() not in address_set:
+            _update_mem_use(self.fp16_grad.payload)
             address_set.add(self.fp16_grad.data_ptr())
 
-        if self.fp32_grad is not None and self.fp32_grad.data_ptr() not in address_set:
-            _update_mem_use(self.fp32_grad)
+        if not self.fp32_grad.is_null() and self.fp32_grad.data_ptr() not in address_set:
+            _update_mem_use(self.fp32_grad.payload)
             address_set.add(self.fp32_grad.data_ptr())
 
         if self.param.data is not None and self.param.data.data_ptr() not in address_set:

colossalai/zero/sharded_param/sharded_tensor.py

@@ -1,30 +1,30 @@
 import torch
 import torch.distributed as dist
 from typing import Optional
+from colossalai.zero.sharded_param.tensorful_state import StatefulTensor, TensorState
 
 
-class ShardedTensor(object):
+class ShardedTensor(StatefulTensor):
 
     def __init__(self, tensor: torch.Tensor, process_group: Optional[dist.ProcessGroup] = None) -> None:
         r"""
         A tensor sharded in multiple processes. Constructed from an existing torch.Tensor instance.
         """
-        self._payload = tensor
-        self.process_group = process_group
-        self.world_size = dist.get_world_size(self.process_group)
-        self.local_rank = dist.get_rank(self.process_group)
-        self._is_sharded = False
+        super().__init__(tensor)
+        self.trans_state(TensorState.HOLD)
 
         self._origin_shape = tensor.shape
         self._origin_numel = tensor.numel()
         self._origin_dtype = tensor.dtype
 
+        self._is_sharded = False
+
     @property
-    def origin_numel(self):
+    def origin_numel(self) -> int:
         return self._origin_numel
 
     @property
-    def origin_shape(self):
+    def origin_shape(self) -> int:
         return self._origin_shape
 
     @property
@@ -34,33 +34,3 @@ class ShardedTensor(object):
     @is_sharded.setter
     def is_sharded(self, flag: bool):
         self._is_sharded = flag
-
-    @property
-    def payload(self):
-        return self._payload
-
-    def copy_payload(self, tensor):
-        self._payload.view(-1).copy_(tensor.view(-1))
-
-    def reset_payload(self, tensor):
-        del self._payload
-        self._payload = tensor
-
-    @property
-    def device(self):
-        return self._payload.device
-
-    @property
-    def dtype(self):
-        assert self._payload.dtype == self._origin_dtype
-        return self._origin_dtype
-
-    def to(self, device: torch.device):
-        raise RuntimeError("Use colo_model_tensor_move install of call .to() on ShardedTensor")
-
-    def to_(self, device: torch.device):
-        raise RuntimeError("Use colo_model_tensor_move install of call .to_() on ShardedTensor")
-
-    @property
-    def shape(self):
-        return self._payload.shape

colossalai/zero/sharded_param/tensorful_state.py

@@ -0,0 +1,81 @@
+from enum import Enum
+from logging import NullHandler
+import torch
+
+
+class TensorState(Enum):
+    FREE = 0
+    HOLD = 1
+    HOLD_AFTER_FWD = 2
+    HOLD_AFTER_BWD = 3
+
+
+class StatefulTensor(object):
+    """A Structure stores a Torch Tensor and labeled states.
+
+    PatrickStar: Parallel Training of Pre-trained Models via Chunk-based Memory Management
+
+    https://arxiv.org/abs/2108.05818
+    """
+
+    def __init__(self, tensor: torch.Tensor, state: TensorState = TensorState.HOLD) -> None:
+        self._state = state
+        if state is not TensorState.FREE:
+            self._payload = tensor
+        else:
+            self._payload = None
+
+    def data_ptr(self):
+        if self._payload is None:
+            return None
+        return self._payload.data_ptr()
+
+    @property
+    def state(self) -> TensorState:
+        return self._state
+
+    def set_null(self) -> None:
+        self._state = TensorState.FREE
+        self._payload = None
+
+    def is_null(self) -> bool:
+        if self._state == TensorState.FREE:
+            assert self._payload is None
+            return True
+        return False
+
+    def trans_state(self, state: TensorState) -> None:
+        self._state = state
+        if state == TensorState.FREE:
+            self._payload = None
+
+    @property
+    def payload(self) -> int:
+        return self._payload
+
+    def copy_payload(self, tensor) -> int:
+        self._payload.view(-1).copy_(tensor.view(-1))
+
+    def reset_payload(self, tensor) -> int:
+        del self._payload
+        self._payload = tensor
+        self.trans_state(TensorState.HOLD)
+
+    @property
+    def device(self) -> torch.device:
+        return self._payload.device
+
+    @property
+    def dtype(self) -> torch.dtype:
+        assert self._payload.dtype == self._origin_dtype
+        return self._origin_dtype
+
+    def to(self, device: torch.device):
+        raise RuntimeError("Use colo_model_tensor_move install of call .to() on ShardedTensor")
+
+    def to_(self, device: torch.device):
+        raise RuntimeError("Use colo_model_tensor_move install of call .to_() on ShardedTensor")
+
+    @property
+    def shape(self):
+        return self._payload.shape

tests/test_zero_data_parallel/test_shard_param.py

@@ -12,6 +12,7 @@ from colossalai.zero.sharded_param import ShardedTensor
 from colossalai.zero.sharded_param.sharded_param import ShardedParamV2
 from colossalai.testing import rerun_on_exception
 from tests.test_zero_data_parallel.common import CONFIG, allclose
+from colossalai.zero.sharded_param.tensorful_state import StatefulTensor
 
 
 @parameterize("shard_strategy_class", [TensorShardStrategy, BucketTensorShardStrategy])
@@ -52,7 +53,7 @@ def _run_shard_param_v2(rank, world_size, port):
     allclose(sparam.sharded_data_tensor.payload, param_ref.data)
 
     # Test get memory usage
-    sparam.fp32_grad = torch.randn(2, 3)
+    sparam.fp32_grad = StatefulTensor(torch.randn(2, 3))
     cuda_mem_use, cpu_mem_use = sparam.get_memory_usage()
     assert cpu_mem_use == 2 * 3 * 4 * 2, f"cpu_mem_use: {cpu_mem_use}"
 
@@ -62,13 +63,13 @@ def _run_shard_param_v2(rank, world_size, port):
     # 4 is size of dummy tensor of param.data
     assert cpu_mem_use == 2 * 3 * 4 * 2 + 4
 
-    sparam.fp16_grad = torch.randn(2, 3).cuda().half()
+    sparam.fp16_grad = StatefulTensor(torch.randn(2, 3).cuda().half())
     cuda_mem_use, cpu_mem_use = sparam.get_memory_usage()
     assert cpu_mem_use == 2 * 3 * 4 * 2 + 4
     assert cuda_mem_use == 2 * 3 * 2
 
-    sparam.fp16_grad = None
-    sparam.fp32_grad = torch.randn(2, 3)
+    sparam.fp16_grad = StatefulTensor(None)
+    sparam.fp32_grad = StatefulTensor(torch.randn(2, 3))
     sparam.remove_torch_payload()
     cuda_mem_use, cpu_mem_use = sparam.get_memory_usage()
     assert cpu_mem_use == 2 * 3 * 4 * 2 + 4
@@ -82,7 +83,7 @@ def _run_shard_param_v2(rank, world_size, port):
     assert cuda_mem_use == 0
 
     # reuse torch grad for sparam
-    sparam.fp32_grad = param.grad
+    sparam.fp32_grad = StatefulTensor(param.grad)
     cuda_mem_use, cpu_mem_use = sparam.get_memory_usage()
     assert cpu_mem_use == 2 * 3 * 4 * 2
     assert cuda_mem_use == 0