rm MdUpdt chain merge (#1135)

* rm MdUpdt chain merge

* use area_id == kMdUpdtArea

* rm judgement

* refine IsSubset


Former-commit-id: f9fe1ee0

oneflow/core/graph/chain_graph.cpp

@@ -79,6 +79,9 @@ void ChainMerger::InitChains() {
 }
 
 bool ChainMerger::DoMerge(std::list<ChainIt>& chains, ChainIt rhs) {
+  CHECK_EQ(rhs->nodes.size(), 1);
+  // rm kMdUpdtArea chain merge
+  if (rhs->nodes.front()->area_id() == kMdUpdtArea) { return false; }
   for (auto chains_it = chains.rbegin(); chains_it != chains.rend(); ++chains_it) {
     ChainIt lhs = *chains_it;
     if (IsSubset(lhs, rhs)) {

oneflow/core/graph/task_node.cpp

@@ -142,10 +142,6 @@ int64_t TaskNode::MemZoneId121() const {
 
 void TaskNode::BuildCtrlRegstDescIfNeed(TaskNode* dst_node) {
   if (IsMeaningLess() || dst_node->IsMeaningLess()) { return; }
-  if (!Global<JobDesc>::Get()->IsTrain() && GetTaskType() == kNormalMdUpdt
-      && dst_node->GetTaskType() == kNormalMdUpdt) {
-    return;
-  }
   const auto& dst_ancestors = dst_node->ancestors();
   if (dst_ancestors.find(this) != dst_ancestors.end()) return;
   BuildCtrlRegstDesc(dst_node);