See how NMTUsage::total_committed uses _vm_total.reserved instead of _vm_total.committed:
```
size_t NMTUsage::total_reserved() const {
  return _malloc_total + _vm_total.reserved;
}

size_t NMTUsage::total_committed() const {
  return _malloc_total + _vm_total.reserved;
}

size_t NMTUsage::reserved(MEMFLAGS flag) const {
  int index = NMTUtil::flag_to_index(flag);
  return _malloc_by_type[index] + _vm_by_type[index].reserved;
}

size_t NMTUsage::committed(MEMFLAGS flag) const {
  int index = NMTUtil::flag_to_index(flag);
  return _malloc_by_type[index] + _vm_by_type[index].committed;
}
```