#!/usr/bin/env python # coding: utf-8 import torch import torch.nn as nn from colossalai.tensor import ColoParameter, ColoTensor import types import inspect from typing import List, Callable from colossalai.utils.model.utils import substitute_init_recursively class LazyInitContext(): """ A context to allow for lazy weight initialization of PyTorch modules. It intercepts the tensor initialization functions for lazy initialization Note: This API is only experimental and subject to future changes. Usage: with LazyInitContext() as ctx: model = nn.Linear(10, 10) model.weight.zero_() # make sure the weight is a meta tensor assert model.weight.is_meta # initialize weights ctx.lazy_init_parameters(model) # make sure the weight is not a meta tensor # and initialized correctly assert not model.weight.is_meta and torch.all(model.weight == 0) Args: to_meta (bool): optional, whether to initialize the model with meta tensors, default is False. extra_torch_tensor_func (List[str]): extra torch tensor functions related to value setting, such as `zero_` and `triu_`. `zero_` is pre-added by default. """ tensor_set_value_func = ['zero_', 'fill_'] def __init__(self, to_meta: bool = False, extra_torch_tensor_func: List[str] = None): # TODO: hijack the torch constructor functions as well self._to_meta = to_meta self._intercepted_nn_init_func_cache = {} self._nn_init_methods = self._get_nn_init_methods() self._torch_mod_cls = torch.nn.modules.module.Module if extra_torch_tensor_func: # use tuple to remove duplicates self._torch_tensor_funcs = tuple(self.tensor_set_value_func + extra_torch_tensor_func) else: self._torch_tensor_funcs = self.tensor_set_value_func @property def to_meta(self): return self._to_meta def _cache_init_func(self, func): """ This method wraps the ``torch.nn.init`` method and torch tensor value-setting functions so that the function call is cached instead of being executed. """ def wrapped_init_func(tensor, *args, **kwargs): if tensor not in self._intercepted_nn_init_func_cache: self._intercepted_nn_init_func_cache[tensor] = [] self._intercepted_nn_init_func_cache[tensor].append((func, args, kwargs)) return wrapped_init_func def _get_nn_init_methods(self): """ This method looks for all available functions in the ``torch.nn.init`` module. """ nn_init_method_names = dir(torch.nn.init) nn_init_methods = [] # look for all methods in ``torch.nn.init`` module for name in nn_init_method_names: nn_init_methods.append((name, getattr(torch.nn.init, name))) def _is_init_method(item): name, func = item if (not isinstance(func, types.FunctionType) or name.startswith('_') or not name.endswith('_')): return False else: return True # remove methods which are not init functions nn_init_methods = list(filter(_is_init_method, nn_init_methods)) return nn_init_methods def _wrap_module_init(self, func): """ This method wraps the calls to the `__init__` of ``torch.nn.Module`` and replaces the argument device with value 'meta' so that all modules are created as meta tensors. """ has_device = 'device' in inspect.signature(func).parameters def layer_lazy_init(module, *args, **kwargs): # if this module contains device argument # we set it to meta to initialize as meta backend if has_device: kwargs['device'] = 'meta' func(module, *args, **kwargs) # if device is not found, we intialize it and convert to meta if not has_device: module.to('meta') return layer_lazy_init def _get_tmp_origin_func_ref(self, name): """ Generate a function name for consistency during caching and retrieving. """ return f'_orig_{name}' def _patch_nn_init_funcs(self): # patch nn.init functions for name, func in self._nn_init_methods: setattr(torch.nn.init, name, self._cache_init_func(func)) def _unpatch_nn_init_funcs(self): # unpatch nn.init functions for name, func in self._nn_init_methods: setattr(torch.nn.init, name, func) def _patch_submodule_init(self): # patch classes __init__ methods def _activate_wrap_init(cls): cls.__orig_init__ = cls.__init__ cls.__init__ = self._wrap_module_init(cls.__init__) substitute_init_recursively(self._torch_mod_cls, _activate_wrap_init) def _unpatch_submodule_init(self): def _recover_orig_init(cls): cls.__init__ = cls.__orig_init__ substitute_init_recursively(self._torch_mod_cls, _recover_orig_init) def _patch_torch_tensor_funcs(self): # patch tensor value-setting functions for func_name in self._torch_tensor_funcs: origin_func_name = self._get_tmp_origin_func_ref(func_name) origin_func = getattr(torch.Tensor, func_name) setattr(torch.Tensor, origin_func_name, origin_func) setattr(torch.Tensor, func_name, self._cache_init_func(origin_func)) def _unpatch_torch_tensor_funcs(self): for func_name in self._torch_tensor_funcs: origin_func_name = self._get_tmp_origin_func_ref(func_name) origin_func = getattr(torch.Tensor, origin_func_name) setattr(torch.Tensor, func_name, origin_func) def __enter__(self): self._patch_torch_tensor_funcs() self._patch_nn_init_funcs() if self._to_meta: self._patch_submodule_init() return self def __exit__(self, *args, **kwargs): if self._to_meta: self._unpatch_submodule_init() self._unpatch_nn_init_funcs() self._unpatch_torch_tensor_funcs() def lazy_init_parameters(self, model: torch.nn.Module, device='cpu'): """ Initialize the weights of the meta-tensor model. Args: model (`torch.nn.Module`): the model instantiated under the context. device (str): the device on which weights are initialized """ def _init_recursively(module: nn.Module): # recursively initialize the module for mod in module.children(): _init_recursively(mod) # initialize and shard tensors directly attached to the current module for name, param in module.named_parameters(recurse=False): _init_and_shard(module, name, param) for name, buf in module.named_buffers(recurse=False): _init_and_shard(module, name, buf) @torch.no_grad() def _init_and_shard(module, name, tensor): # check whether the tensor is a buffer or parameter is_param = isinstance(tensor, nn.parameter.Parameter) # get sharding spec dist_spec = getattr(tensor, 'dist_spec', None) pg = getattr(tensor, 'pg', None) comp_spec = getattr(tensor, 'comp_spec', None) # convert the tensor from meta to materialized one if tensor.is_meta: materialized_tensor = torch.empty_like(tensor, device=device) # if this tensor is a meta tensor, it must have an init function assert tensor in self._intercepted_nn_init_func_cache tensor = materialized_tensor # apply init function if tensor in self._intercepted_nn_init_func_cache: init_func, args, kwargs = self._intercepted_nn_init_func_cache[tensor][-1] init_func(tensor, *args, **kwargs) # convert it to ColoTensor or ColoParameter if is_param: tensor = ColoParameter.from_torch_tensor(tensor, requires_grad=tensor.requires_grad) else: tensor = ColoTensor.from_torch_tensor(tensor) # override the original tensor with torch.no_grad(): setattr(module, name, tensor) # apply sharding if dist_spec: tensor.process_group = pg tensor.set_tensor_spec(dist_spec, comp_spec) _init_recursively(model) return model