mirror of https://github.com/hpcaitech/ColossalAI
77 lines
2.6 KiB
Python
77 lines
2.6 KiB
Python
import torch
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from torch.utils._pytree import tree_map, tree_flatten
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__all__ = ['MetaTensor']
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class MetaTensor(torch.Tensor):
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"""
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A wrapping tensor that hacks `torch.autograd` without patching more `torch.ops.aten` ops.
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`fake_device` is the device that `MetaTensor` is supposed to run on.
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"""
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_tensor: torch.Tensor
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__slots__ = ['_tensor']
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@staticmethod
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def __new__(cls, elem, fake_device=None):
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# The wrapping tensor (MetaTensor) shouldn't hold any
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# memory for the class in question, but it should still
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# advertise the same device as before
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r = torch.Tensor._make_wrapper_subclass(
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cls,
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elem.size(),
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strides=elem.stride(),
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storage_offset=elem.storage_offset(),
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dtype=elem.dtype,
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layout=elem.layout,
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device=fake_device if fake_device is not None else elem.device,
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requires_grad=elem.requires_grad) # deceive the frontend for aten selections
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r._tensor = elem
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# ...the real tensor is held as an element on the tensor.
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if not r._tensor.is_meta:
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r._tensor = r._tensor.to(torch.device('meta'))
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# only tensor not on `meta` should be copied to `meta`
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return r
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def __repr__(self):
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if self.grad_fn:
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return f"MetaTensor({self._tensor}, fake_device='{self.device}', grad_fn={self.grad_fn})"
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return f"MetaTensor({self._tensor}, fake_device='{self.device}')"
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@classmethod
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def __torch_dispatch__(cls, func, types, args=(), kwargs=None):
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fake_device = None
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def unwrap(x):
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nonlocal fake_device
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if isinstance(x, MetaTensor):
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fake_device = x.device
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x = x._tensor
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elif isinstance(x, torch.Tensor):
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fake_device = x.device
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x = x.to(torch.device('meta'))
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return x
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if 'device' in kwargs:
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fake_device = kwargs['device']
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kwargs['device'] = torch.device('meta')
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args = tree_map(unwrap, args)
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kwargs = tree_map(unwrap, kwargs)
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# run aten for backend=CPU but actually on backend=Meta
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out = func(*args, **kwargs)
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# Now, we want to continue propagating this tensor, so we rewrap Tensors in
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# our custom tensor subclass
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def wrap(x):
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if isinstance(x, torch.Tensor):
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nonlocal fake_device
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if not x.is_meta:
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x = x.to(torch.device('meta'))
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return MetaTensor(x, fake_device=fake_device) if isinstance(x, torch.Tensor) else x
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return tree_map(wrap, out)
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