from enum import Enum from typing import Dict, Optional import torch import torch.distributed as dist import torch.nn as nn from colossalai.amp.naive_amp._fp16_optimizer import DynamicGradScaler from colossalai.context.parallel_mode import ParallelMode from colossalai.core import global_context as gpc from colossalai.nn.optimizer import ColossalaiOptimizer from colossalai.zero.shard_utils import BaseShardStrategy from colossalai.zero.sharded_model import ShardedModelV2 from colossalai.zero.sharded_model._zero3_utils import cast_tensor_to_fp32 from torch import Tensor from torch.distributed import ProcessGroup from torch.nn.parameter import Parameter from torch.optim import Optimizer from ._utils import has_inf_or_nan class OptimState(Enum): SCALED = 1 UNSCALED = 2 class ShardedOptimizerV2(ColossalaiOptimizer): def __init__(self, optimizer: Optimizer, sharded_model: ShardedModelV2, shard_strategy: BaseShardStrategy, cpu_offload: bool = False, initial_scale: float = 2**32, min_scale: float = 1, growth_factor: float = 2, backoff_factor: float = 0.5, growth_interval: float = 1000, hysteresis: float = 2, max_scale: int = 2**32, dp_process_group: Optional[ProcessGroup] = None, mp_process_group: Optional[ProcessGroup] = None) -> None: assert isinstance(sharded_model, ShardedModelV2), 'model must be wrapped with ShardedModel' super().__init__(optimizer) self.shard_strategy = shard_strategy self.model: ShardedModelV2 = sharded_model 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) self.mp_process_group = mp_process_group or gpc.get_group(ParallelMode.MODEL) # Grad scaler self.grad_scaler = DynamicGradScaler(initial_scale=initial_scale, min_scale=min_scale, growth_factor=growth_factor, backoff_factor=backoff_factor, growth_interval=growth_interval, hysteresis=hysteresis, max_scale=max_scale) self._found_overflow: Tensor = torch.FloatTensor([0]).to(torch.cuda.current_device()) # Store fp32 param shards self.master_params: Dict[Parameter, Tensor] = {} for group in optimizer.param_groups: for p in group['params']: assert hasattr(p, 'col_attr'), 'The parameter must be wrapped with ShardedParam' is_param_sharded = p.col_attr.data.is_sharded if not is_param_sharded: # TODO (ver217): we may not use shard / gather here # Param is no sharded, which means we use ZeRO-2 here # As we only store param shard, we shard it here self.shard_strategy.shard([p.col_attr.data]) self.master_params[p] = cast_tensor_to_fp32(p.col_attr.data.payload).to(self.device) if not is_param_sharded: # In this branch, there's no need to shard param # So we gather here self.shard_strategy.gather([p.col_attr.data]) def step(self, *args, **kwargs): # unscale grads if scaled if self.optim_state == OptimState.SCALED: self._unscale_grads() found_inf = self._check_overflow() self.grad_scaler.update(found_inf) if found_inf: self.zero_grad() return # Write master param to p.data for group in self.optim.param_groups: for p in group['params']: p.data = self.master_params[p] # Now p.data is sharded # So optimizer states are sharded naturally ret = self.optim.step(*args, **kwargs) # Write master param to payload for group in self.optim.param_groups: for p in group['params']: is_param_sharded = p.col_attr.data.is_sharded if not is_param_sharded: # We use ZeRO-2 here # The `p.col_attr.data` 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.col_attr.data]) # We have to use `copy_payload` instead of `reset_payload` # Since p.data is fp32 and p.col_attr.data is fp16 p.col_attr.data.copy_payload(p.data) if not is_param_sharded: # We gather full fp16 param here self.shard_strategy.gather([p.col_attr.data]) p.data = p.col_attr.data.payload 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) # check for overflow for group in self.optim.param_groups: for p in group['params']: if has_inf_or_nan(p.grad): self._found_overflow.fill_(1.0) break # all-reduce across dp group dist.all_reduce(self._found_overflow, op=dist.ReduceOp.MAX, group=self.dp_process_group) # all-reduce over model parallel group dist.all_reduce(self._found_overflow, op=dist.ReduceOp.MAX, group=self.mp_process_group) return self._found_overflow.item() > 0 def _unscale_grads(self): assert self.optim_state == OptimState.SCALED for group in self.optim.param_groups: for p in group['params']: if p.grad is not None: p.grad.data.div_(self.loss_scale) self.optim_state = OptimState.UNSCALED def zero_grad(self, *args, **kwargs): # We must set grad to None # Because we will judge whether local grad accumulation # is enabled by wheter grad is None self.optim.zero_grad(set_to_none=True)