RFR: 8319876: Reduce memory consumption of VM_ThreadDump::doit [v2]

[Stefan Karlsson]

On Mon, 13 Nov 2023 10:51:30 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> `ThreadStackTrace::_jni_locked_monitors` and `ThreadStackTrace::_frames` are both `GrowableArray`, and IIUC its backing memory lives in RA as well. At least `_frames` will get added to inside your ResourceMark via `add_stack_frame`.

>From what I can see these two are CHeap-allocated:

ThreadStackTrace::ThreadStackTrace(JavaThread* t, bool with_locked_monitors) {
  _thread = t;
  _frames = new (mtServiceability) GrowableArray<StackFrameInfo*>(INITIAL_ARRAY_SIZE, mtServiceability);
  _depth = 0;
  _with_locked_monitors = with_locked_monitors;
  if (_with_locked_monitors) {
    _jni_locked_monitors = new (mtServiceability) GrowableArray<OopHandle>(INITIAL_ARRAY_SIZE, mtServiceability);
  } else {
    _jni_locked_monitors = nullptr;
  }
}

The MEMFLAGS indicate that they are CHeap-allocated.

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PR Comment: https://git.openjdk.org/jdk/pull/16598#issuecomment-1807952360