Method ClearExcess

include/xgboost/cache.h:102–112

  }

  void ClearExcess() {
    this->CheckConsistent();
    // clear half of the entries to prevent repeatingly clearing cache.
    std::size_t half_size = max_size_ / 2;
    while (queue_.size() >= half_size && !queue_.empty()) {
      auto p_fmat = queue_.front();
      queue_.pop();
      container_.erase(p_fmat);
    }
    this->CheckConsistent();
  }

 public:
  /**