[GitHub] [incubator-mxnet] barry-jin commented on a change in pull request #20462: [BUGFIX] Fix #20293

[GitBox <gi...@apache.org>]

barry-jin commented on a change in pull request #20462:
URL: https://github.com/apache/incubator-mxnet/pull/20462#discussion_r673515352



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File path: src/imperative/cached_op.cc
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@@ -989,7 +991,12 @@ void CachedOp::StaticBackward(
       auto entry = state.info.grad_graph.outputs[iter->second];
       if (!idx.exist(entry.node.get())) continue;
       auto eid = idx.entry_id(entry);
-      state.array_reqs[eid] = reqs[iter->second];
+      // if ref count is not 0, then we should not assign req user provide
+      if (reqs[iter->second] == kNullOp && !(ref_count[eid] == 0)) {
+        state.array_reqs[eid] = kWriteTo;

Review comment:
       Yes, we need to put `kWriteTo` here. Because memory plan already happens in [SetBackwardGraph](https://github.com/apache/incubator-mxnet/blob/3480ba2c6df02bb907d3a975d354efa8697c4e71/src/imperative/cached_op.cc#L259) before this. Here we get the updated ref_count from the graph and modify the req_types based on the ref_count.  




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