C:\Temp>type repro.cpp
#include <memory_resource>
#include <vector>
#include <iostream>

struct logging_resource : public std::pmr::memory_resource
{
 void* do_allocate(std::size_t bytes, std::size_t alignment) override
 {
   log.push_back(bytes);
   return std::pmr::new_delete_resource()->allocate(bytes, alignment);
 }

 void do_deallocate(void* p, std::size_t bytes, std::size_t alignment) override
 {
   std::pmr::new_delete_resource()->deallocate(p, bytes, alignment);
 }

 bool do_is_equal(const std::pmr::memory_resource& other)
   const noexcept override
 {
   return this == &other;
 }

  std::vector<ptrdiff_t> log;
};

int main()
{
  logging_resource upstream;
  std::pmr::pool_options options = {
    .max_blocks_per_chunk = 1,
    .largest_required_pool_block = 0};
  std::pmr::unsynchronized_pool_resource res(options, &upstream);

  size_t size = 0x8001;
  void* p = res.allocate(size);

  for (auto e : upstream.log) std::cout << std::hex << "0x" << e << std::endl;

  res.deallocate(p, size);

  return 0;
}

C:\Temp>cl test.cpp /EHsc /std:c++20
Microsoft (R) C/C++ Optimizing Compiler Version 19.32.31335 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

repro.cpp
Microsoft (R) Incremental Linker Version 19.32.31335
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:repro.exe
repro.obj

C:\Temp>.\repro.exe
0x30
0x40038