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.grad_scaler import DynamicGradScaler from colossalai.context.parallel_mode import ParallelMode from colossalai.core import global_context as gpc from colossalai.logging import get_dist_logger from colossalai.nn.optimizer import ColossalaiOptimizer 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): """A wrapper for optimizer. `ShardedOptimizerV2` and `ShardedModelV2` implement Zero Redundancy Optimizer (ZeRO) stage 3. You must use `ShardedOptimizerV2` with `ShardedModelV2`. Args: sharded_model (ShardedModelV2): A sharded model initialized by class ShardedModelV2. The optimizer will use the shard strategy provided by sharded model to shard param fp32 tensors. optimizer (Optimizer): An Optimizer instance. cpu_offload (bool, optional): Is offloading the optimizer states to CPU.. Defaults to False. gpu_margin_mem_ratio (float, optional): The ratio of GPU remaining memory (after the first forward-backward) which will be used when using hybrid CPU optimizer. Defaults to 0.0. initial_scale (float, optional): Initial scale used by DynamicGradScaler. Defaults to 2**32. min_scale (float, optional): Min scale used by DynamicGradScaler. Defaults to 1. growth_factor (float, optional): growth_factor used by DynamicGradScaler. Defaults to 2. 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. 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. """ def __init__(self, sharded_model: ShardedModelV2, optimizer: Optimizer, cpu_offload: bool = False, gpu_margin_mem_ratio: float = 0.0, 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 = sharded_model.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.gpu_margin_mem_ratio: float = float(gpu_margin_mem_ratio) assert 0.0 <= self.gpu_margin_mem_ratio <= 1.0, f'gpu_margin_mem_ratio must >=0.0 and <=1.0' # Only move fp32 shards from CPU to GPU when user allows and inner optimizer is valid # Inner optimizer must support optimizing hybrid (CPU and CUDA) tensors, # and it must set `num_fp32_shards_per_param` correctly self._should_move_fp32_shards_h2d: bool = cpu_offload and self.gpu_margin_mem_ratio > 0.0 and getattr( optimizer, 'num_fp32_shards_per_param', 0) >= 2 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()) self._logger = get_dist_logger() # Store fp32 param shards self.master_params: Dict[Parameter, Tensor] = {} for group in self.optim.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.sharded_data_tensor.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.sharded_data_tensor], self.dp_process_group) self.master_params[p] = cast_tensor_to_fp32(p.col_attr.sharded_data_tensor.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.sharded_data_tensor], self.dp_process_group) def step(self, *args, **kwargs): if self._should_move_fp32_shards_h2d: self._should_move_fp32_shards_h2d = False available_cuda_margin_mem = self.model.cuda_margin_space * self.gpu_margin_mem_ratio fp32_shards_available_cuda_margin_mem = available_cuda_margin_mem / self.optim.num_fp32_shards_per_param fp32_shards_used_cuda_margin_mem = 0 for group in self.optim.param_groups: for p in group['params']: shard_mem = self.master_params[p].numel() * self.master_params[p].element_size() if fp32_shards_used_cuda_margin_mem + shard_mem < fp32_shards_available_cuda_margin_mem: self.master_params[p] = self.master_params[p].to(torch.cuda.current_device()) p.grad.data = p.grad.data.to(torch.cuda.current_device()) p.col_attr.offload_fp32_grad = False fp32_shards_used_cuda_margin_mem += shard_mem # 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._logger.info('found inf during ShardedOptimV2 step') self.zero_grad() return # assign master param pointers to p.data. # We will not trigger data copy here. 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) # Copy master param data (fp32) to payload of col_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.col_attr.sharded_data_tensor.is_sharded if not is_param_sharded: # We use ZeRO-2 here # The `p.col_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.col_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.col_attr.sharded_data_tensor is fp16 # TODO() optimize this line CPU (fp32) -> GPU (fp16) p.col_attr.sharded_data_tensor.copy_payload(p.data) if not is_param_sharded: # We gather full fp16 param here self.shard_strategy.gather([p.col_attr.sharded_data_tensor], self.dp_process_group) p.data = p.col_attr.sharded_data_tensor.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) def sync_grad(self): pass