8319876: Reduce memory consumption of VM_ThreadDump::doit

Reviewed-by: phh
Backport-of: 8ec6b8de3bb3d7aeebdcb45d761b18cce3bab75e

Author: Long Yang

src/hotspot/share/runtime/vmOperations.cpp

@@ -230,7 +230,6 @@ VM_ThreadDump::VM_ThreadDump(ThreadDumpResult* result,
   _result = result;
   _num_threads = 0; // 0 indicates all threads
   _threads = nullptr;
-  _result = result;
   _max_depth = max_depth;
   _with_locked_monitors = with_locked_monitors;
   _with_locked_synchronizers = with_locked_synchronizers;
@@ -245,7 +244,6 @@ VM_ThreadDump::VM_ThreadDump(ThreadDumpResult* result,
   _result = result;
   _num_threads = num_threads;
   _threads = threads;
-  _result = result;
   _max_depth = max_depth;
   _with_locked_monitors = with_locked_monitors;
   _with_locked_synchronizers = with_locked_synchronizers;

src/hotspot/share/services/threadService.cpp

@@ -696,7 +696,7 @@ void ThreadStackTrace::dump_stack_at_safepoint(int maxDepth, ObjectMonitorsView*
                         RegisterMap::UpdateMap::include,
                         RegisterMap::ProcessFrames::include,
                         RegisterMap::WalkContinuation::skip);
-
+    ResourceMark rm;
     // If full, we want to print both vthread and carrier frames
     vframe* start_vf = !full && _thread->is_vthread_mounted()
       ? _thread->carrier_last_java_vframe(&reg_map)