leezu commented on a change in pull request #20559:
URL: https://github.com/apache/incubator-mxnet/pull/20559#discussion_r701074106
##########
File path: tests/python/unittest/test_autograd.py
##########
@@ -519,3 +519,110 @@ def test_gradient():
dx.backward()
assert abs(x.grad.asscalar() - 2.71828175) < 1e-7
+def test_retain_grad_drop_grad():
+ x = nd.array([1,2,3,4])
+ x.attach_grad()
+ y = nd.array([5,6,7,8])
+ y.attach_grad()
+
+ with mx.autograd.record():
+ u = x * y
+ z = u * x
+
+ u.attach_grad()
+ z.attach_grad()
+ out_grad = nd.array([10, 10, 10, 10])
+ z.backward(out_grad, retain_graph=True)
+
+ assert (u.grad == out_grad * x).asnumpy().all()
+ assert (z.grad == out_grad).asnumpy().all()
+ assert (x.grad == out_grad * 2 * x * y).asnumpy().all()
+ assert (y.grad == out_grad * x*x).asnumpy().all()
+
+ u.drop_grad()
+ z.drop_grad()
+ y.drop_grad()
+ out_grad = nd.array([0.1, 0.1, 0.1, 0.1])
+ z.backward(out_grad)
+
+ assert u.grad is None and z.grad is None and y.grad is None
+ assert (x.grad == out_grad * 2 * x * y).asnumpy().all()
+
+def test_retain_grad_drop_grad_gluon():
+ class CompBlock(mx.gluon.HybridBlock):
+ def __init__(self):
+ super().__init__()
+
+ def forward(self, a, b):
+ out1 = a*b
+ out2 = out1 * a
+ self.mark_vars(out1)
+ return out2
+
+ x = mx.np.array([1,2,3,4])
+ y = mx.np.array([5,6,7,8])
+ x.attach_grad()
+ y.attach_grad()
+ block2 = CompBlock()
+ block2.initialize()
+ # block2.hybridize()
Review comment:
Should this test be run both with and without hybridize? You can
parameterize the test function https://docs.pytest.org/en/6.2.x/parametrize.html
##########
File path: src/imperative/imperative_utils.cc
##########
@@ -166,6 +167,16 @@ void RunGraph(
if (callback) {
mxnet::common::ExecuteMonOutputCallback(idx, arrays, i, callback);
}
+ // set the autograd_entry_ in marked nleafs
+ if (nleafs.size()) {
+ auto it = node.source->attrs.dict.find("mark_id");
+ if (it != node.source->attrs.dict.end()) {
+ int mark_id = std::stoi(it->second);
+ CHECK_LT(mark_id, nleafs.size())
+ << "Mark_id exceeds the nonleaf list size.";
+ nleafs[mark_id]->copy_autograd_entry_(ndoutputs[0]);
Review comment:
Have you verified this is correct if a marked variable has multiple
outputs? I see your test case below only considers variables with a single
output:
```
def forward(self, a, b):
out1 = a*b
out2 = out1 * a
self.mark_vars(out1)
return out2
```
##########
File path: python/mxnet/gluon/block.py
##########
@@ -1635,6 +1637,50 @@ def reset_ctx(self, ctx):
for p in params.values():
p.reset_ctx(ctx)
+ def mark_vars(self, var_arrays):
+ """Mark the intermediate nodes for autograd computation.
+
+ Parameters
+ ----------
+ vars : ndarrays or List[ndarrays]
+ The marked arrays used in deferredcomputation
+ """
+ if not self._active:
+ var_arrays = _as_list(var_arrays)
+ self._nleaf_vars.extend(var_arrays)
+ else:
+ prev_val = dc.set_deferred_compute(False)
+ var_arrays = _as_list(var_arrays)
+ # Prepare ctypes array types
+ import ctypes
+ var_handles_type = ctypes.c_void_p * len(var_arrays)
+ # Convert handles
+ var_handles = var_handles_type(*[arr.handle for arr in var_arrays])
+ check_call(_LIB.MXNDArrayMarkDCVariables(var_handles,
len(var_arrays), len(self._nleaf_vars)))
+ self._nleaf_vars.extend(var_arrays)
+ dc.set_deferred_compute(prev_val)
+
+ def get_mark_vars(self, mark_ids):
+ """Retrieve the marked ndarrays according to the order by which they
are marked.
+
+ Parameters
+ ----------
+ mark_ids : int or List[int]
+ The order by which the ndarray is marked.
Review comment:
For some networks, the order or total number of marked arrays could
differ depending on constructor arguments. Would it be simpler to associate a
name to the marked array during `mark_vars()` (eg. `mark_vars(test_grad=var,
test2_grad=var2)` and retrieval via get_mark_vars('test_grad', test2_grad')`?)
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