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

[Thomas Stuefe]

On Mon, 13 Nov 2023 11:09:37 GMT, Stefan Karlsson <stefank 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.

Wait, how does this work on expansion?

`ThreadStackTrace::add_stack_frame` -> `GrowableArray::append` -> ... ->


template <typename E, typename Derived>
void GrowableArrayWithAllocator<E, Derived>::expand_to(int new_capacity) {
...
  E* newData = static_cast<Derived*>(this)->allocate();

Calls `GrowableArray::allocate()` without MEMFLAGS, which calls `GrowableArrayResourceAllocator::allocate`

What am I missing?

---

Update, never mind, I see the big switch in GrowableArray::allocate now.

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PR Comment: https://git.openjdk.org/jdk/pull/16598#issuecomment-1807968870