[fx] added activation checkpointing annotation (#1349)

* [fx] added activation checkpointing annotation

* polish code

* polish code

colossalai/fx/tracer/tracer.py

@@ -8,11 +8,12 @@ import enum
 import inspect
 import functools
 import operator
+from contextlib import contextmanager
 from colossalai.fx.tracer.meta_patch import meta_patched_module
 import torch
 import torch.nn as nn
 from torch import Tensor
-from torch.fx import Tracer
+from torch.fx import Tracer, Node
 from torch.fx.graph import Graph
 from torch.fx.proxy import Proxy, ParameterProxy
 from ..proxy import ColoProxy
@@ -55,11 +56,17 @@ class ColoTracer(Tracer):
         graph = tracer.trace(model, concrete_args={'y': torch.rand(4, 10)}, meta_args={'x': torch.rand(4, 10, device='meta')})
     """
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, trace_act_ckpt: bool = False, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.tracer_type = TracerType.META
         self.proxy_cls = ColoProxy
 
+        # whether the tracer will record the usage of torch.utils.checkpoint
+        self.trace_act_ckpt = trace_act_ckpt
+        # whether the current tracing occurs within the activation checkpoint functions
+        self.inside_torch_checkpoint_func = False
+        self.act_ckpt_region_count = 0
+
     # Feature flag for proxying accesses to buffer values
     proxy_buffer_attributes: bool = True
 
@@ -297,7 +304,10 @@ class ColoTracer(Tracer):
             self.orig_torch_tensor_methods = [val[1] for val in self.patched_torch_tensor_methods.values()]
 
         try:
-            self.graph = super().trace(root, concrete_args=concrete_args)
+            # to track the usage of torch.utils.checkpoint
+            with self.trace_activation_checkpoint(enabled=self.trace_act_ckpt):
+                self.graph = super().trace(root, concrete_args=concrete_args)
+
         finally:
             # recover the patched methods
             for name, (_, orig) in self.patched_torch_tensor_methods.items():
@@ -338,6 +348,43 @@ class ColoTracer(Tracer):
 
         return self.graph
 
+    @contextmanager
+    def trace_activation_checkpoint(self, enabled: bool):
+        if enabled:
+            orig_ckpt_func = torch.utils.checkpoint.CheckpointFunction
+
+            class PatchedCheckpointFunction(torch.autograd.Function):
+
+                @staticmethod
+                def forward(ctx, run_function, preserve_rng_state, *args):
+                    # signal that the current tracing occurs within activaton checkpoint part
+                    self.inside_torch_checkpoint_func = True
+                    out = run_function(*args)
+                    self.inside_torch_checkpoint_func = False
+                    self.act_ckpt_region_count += 1
+                    return out
+
+                @staticmethod
+                def backward(ctx: Any, *grad_outputs: Any) -> Any:
+                    raise NotImplementedError(
+                        "We do not implement the backward pass as we only trace the forward pass.")
+
+            # override the checkpoint function
+            torch.utils.checkpoint.CheckpointFunction = PatchedCheckpointFunction
+        yield
+
+        if enabled:
+            # recover the checkpoint function upon exit
+            torch.utils.checkpoint.CheckpointFunction = orig_ckpt_func
+
+    def create_node(self, *args, **kwargs) -> Node:
+        node = super().create_node(*args, **kwargs)
+
+        if self.inside_torch_checkpoint_func:
+            # annotate the activation checkpoint module
+            setattr(node, 'activation_checkpoint', self.act_ckpt_region_count)
+        return node
+
 
 def wrap_tensor_constructor_method(target):
 
@@ -367,7 +414,7 @@ def wrap_tensor_constructor_method(target):
             colo_proxy = proxy.tracer.create_proxy("call_function", target, args, kwargs)
             if not isinstance(colo_proxy, ColoProxy):
                 meta_out = compute_meta_data_for_functions_proxy(target, args, kwargs)
-                colo_proxy = ColoProxy(fx_proxy.node)
+                colo_proxy = ColoProxy(proxy.node)
                 colo_proxy.meta_data = meta_out
             return colo_proxy
         else:

tests/test_fx/test_tracer/test_activation_checkpoint_annotation.py

@@ -0,0 +1,62 @@
+import torch
+import torch.nn as nn
+from colossalai.fx import ColoTracer
+from torch.fx import GraphModule
+from torch.utils.checkpoint import checkpoint
+
+
+class MLP(torch.nn.Module):
+
+    def __init__(self):
+        super().__init__()
+        self.linear1 = torch.nn.Linear(4, 4)
+        self.linear2 = torch.nn.Linear(4, 4)
+
+    def forward(self, x):
+        x = self.linear1(x)
+        x = self.linear2(x)
+        return x
+
+
+# Simple module for demonstration
+class MyModule(torch.nn.Module):
+
+    def __init__(self):
+        super().__init__()
+        self.mlp_1 = MLP()
+        self.mlp_2 = MLP()
+        self.output = torch.nn.Linear(4, 4)
+
+    def forward(self, x):
+        x = checkpoint(self.mlp_1, x)
+        x = checkpoint(self.mlp_2, x)
+        x = self.output(x)
+        return x
+
+
+def test_activation_checkpoint_annotation():
+    module = MyModule()
+
+    # test tracing with activation checkpoint
+    tracer = ColoTracer(trace_act_ckpt=True)
+    graph = tracer.trace(module)
+    gm = GraphModule(module, graph)
+
+    for node in gm.graph.nodes:
+        if node.name in ['mlp_1_linear1', 'mlp_1_linear2']:
+            assert getattr(node, 'activation_checkpoint', -1) == 0
+
+    for node in gm.graph.nodes:
+        if node.name in ['mlp_2_linear1', 'mlp_2_linear2']:
+            assert getattr(node, 'activation_checkpoint', -1) == 1
+
+    tracer = ColoTracer(trace_act_ckpt=False)
+    graph = tracer.trace(module)
+    gm = GraphModule(module, graph)
+
+    for node in gm.graph.nodes:
+        assert not hasattr(node, 'activation_checkpoint')
+
+
+if __name__ == '__main__':
+    test_activation_checkpoint_annotation()