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# Copyright (c) Microsoft Corporation.
# SPDX-License-Identifier: Apache-2.0
# DeepSpeed Team
#Linear Module to use with ZeRO Stage 3 to allow for parameter memory release
#after the module execution during forward
#Instead of saving variables using save_for_backward, we save variable ids
#Allowing us to retrieve the variable without creating pointer to it
#Which allows for underlying tensor to be garbage collected
#When partitioned as needed by the Zero Stage 3 optimizer
#TODO instead of patching Linear module, we could patch the ctx.save_for_backward
#ctx.saved_tensors so that this approach works for all nn modules that are built upon
#torch.nn.function. However the issue is that many modules uses C++ implementations
#which does not have pytorch implementation. Eg torch.addmm which acts as a functional
#when implemented outside of torch.autograd.Function
import math
import torch
from torch import Tensor
from torch.nn.parameter import Parameter
from torch.nn import init
from torch.nn.modules.module import Module
from deepspeed.runtime.utils import noop_decorator
from deepspeed import comm as dist
from deepspeed.accelerator import get_accelerator
def print_rank_0(message, debug=False, force=False):
if dist.get_rank() == 0 and (debug or force):
print(message)
try:
autocast_custom_fwd = get_accelerator().amp().custom_fwd
autocast_custom_bwd = get_accelerator().amp().custom_bwd
except (ImportError, AttributeError) as exp:
autocast_custom_fwd = noop_decorator
autocast_custom_bwd = noop_decorator
class LinearFunctionForZeroStage3(torch.autograd.Function):
# Note that both forward and backward are @staticmethods
@staticmethod
@autocast_custom_fwd
# bias is an optional argument
def forward(ctx, input, weight, bias=None):
ctx.save_for_backward(input, weight, bias)
if input.dim() == 2 and bias is not None:
# fused op is marginally faster
ret = torch.addmm(bias, input, weight.t())
else:
output = input.matmul(weight.t())
if bias is not None:
output += bias
ret = output
return ret
# This function has only a single output, so it gets only one gradient
@staticmethod
@autocast_custom_bwd
def backward(ctx, grad_output):
# This is a pattern that is very convenient - at the top of backward
# unpack saved_tensors and initialize all gradients w.r.t. inputs to
# None. Thanks to the fact that additional trailing Nones are
# ignored, the return statement is simple even when the function has
# optional inputs.
input, weight, bias = ctx.saved_tensors
grad_input = grad_weight = grad_bias = None
#print(f"backward shaped grad_output {grad_output.shape}, input {input.shape}, weight {weight.shape} and bias {bias.shape if bias is not None else None}")
# These needs_input_grad checks are optional and there only to
# improve efficiency. If you want to make your code simpler, you can
# skip them. Returning gradients for inputs that don't require it is
# not an error.
if ctx.needs_input_grad[0]:
#print(f"Computing grad input weight {weight.shape} grad_output {grad_output.shape}")
grad_input = grad_output.matmul(weight)
#print(f"Computed grad input {grad_input.shape}")
if ctx.needs_input_grad[1]:
#print("Computing grad weight")
dim = grad_output.dim()
if dim > 2:
grad_weight = grad_output.reshape(-1,
grad_output.shape[-1]).t().matmul(input.reshape(-1, input.shape[-1]))
else:
grad_weight = grad_output.t().matmul(input)
#print(f"Computed grad weight grad_weight {grad_weight.shape}")
if bias is not None and ctx.needs_input_grad[2]:
#print("Computing grad bias")
if dim > 2:
grad_bias = grad_output.sum([i for i in range(dim - 1)])
else:
grad_bias = grad_output.sum(0)
#print("Done computing grad bias")
#print("needs bias")
#print(f"backward shaped grad_input {grad_input.shape}, grad_weight {grad_weight.shape}, grad_bias {grad_bias.shape if grad_bias is not None else None}")
return grad_input, grad_weight, grad_bias
def zero3_linear_wrap(input, weight, bias=None):
if bias is None:
return LinearFunctionForZeroStage3.apply(input, weight)
else:
return LinearFunctionForZeroStage3.apply(input, weight, bias)
class LinearModuleForZeroStage3(Module):
r"""Applies a linear transformation to the incoming data: :math:`y = xA^T + b`.
The weights are pre-transposed and stored as A^T instead of transposing during each
forward. Memory savings proportional to the parameter size.
Args:
in_features: size of each input sample
out_features: size of each output sample
bias: If set to ``False``, the layer will not learn an additive bias.
Default: ``True``
Shape:
- Input: :math:`(N, *, H_{in})` where :math:`*` means any number of
additional dimensions and :math:`H_{in} = \text{in\_features}`
- Output: :math:`(N, *, H_{out})` where all but the last dimension
are the same shape as the input and :math:`H_{out} = \text{out\_features}`.
Attributes:
weight: the learnable weights of the module of shape
:math:`(\text{out\_features}, \text{in\_features})`. The values are
initialized from :math:`\mathcal{U}(-\sqrt{k}, \sqrt{k})`, where
:math:`k = \frac{1}{\text{in\_features}}`
bias: the learnable bias of the module of shape :math:`(\text{out\_features})`.
If :attr:`bias` is ``True``, the values are initialized from
:math:`\mathcal{U}(-\sqrt{k}, \sqrt{k})` where
:math:`k = \frac{1}{\text{in\_features}}`
Examples::
>>> m = nn.Linear(20, 30)
>>> input = torch.randn(128, 20)
>>> output = m(input)
>>> print(output.size())
torch.Size([128, 30])
"""
__constants__ = ['in_features', 'out_features']
in_features: int
out_features: int
weight: Tensor
def __init__(self, in_features: int, out_features: int, bias: bool = True) -> None:
super(LinearModuleForZeroStage3, self).__init__()
print("Building ZeRO module")
self.in_features = in_features
self.out_features = out_features
self.weight = Parameter(torch.Tensor(out_features, in_features))
if bias:
self.bias = Parameter(torch.Tensor(out_features))
else:
self.register_parameter('bias', None)
self.reset_parameters()
def reset_parameters(self) -> None:
init.kaiming_uniform_(self.weight, a=math.sqrt(5))
if self.bias is not None:
fan_in, _ = init._calculate_fan_in_and_fan_out(self.weight)
bound = 1 / math.sqrt(fan_in)
init.uniform_(self.bias, -bound, bound)
def forward(self, input: Tensor) -> Tensor:
return LinearFunctionForZeroStage3.apply(input, self.weight, self.bias)
def extra_repr(self) -> str:
return 'in_features={}, out_features={}, bias={}'.format(self.in_features, self.out_features, self.bias
is not None)
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