How to define RAII buffer class with custom memory manager?

The question below can be a general question about design patterns but, due to my lack of knowledge, I couldn't.

I am trying to implement a RAII-style buffer class (Buffer) using a given memory manager class (MemoryManager) with interfaces like open_manager/close_manager/allocate/deallocate etc. The Buffer would look like:

class Buffer {
public:
  explicit Buffer(std::size_t sz) { /* Allocation */ }
  ~Buffer() { /* Deallocation */ }
};

But as a condition, the MemoryManager class needs to be instantiated, which means that the Buffer needs to be able to use the specific manager instance in the destructor.

  ~Buffer() { manager.dealloc(/* ... */); }

There would be several options:

• const MemoryManager* as a Buffer member variable like:

  class Buffer {
  public:
    Buffer(std::size_t sz, const MemoryManager* manager) : manager_(manager) { /*...*/ }
    ~Buffer() { manager_->dealloc(/*...*/); }
  private:
    const MemoryMenager* manager_{nullptr};
  };
  

• const MemoryManager& as a Buffer member variable
• The manager as a global variable

Which options are the best ? or are there any better ways to get this done ?

Thank you.