Pass DMatrix into metric for caching. (#8790)

include/xgboost/cache.h

@@ -32,6 +32,8 @@ class DMatrixCache {
     CacheT& Value() { return *value; }
   };
 
+  static constexpr std::size_t DefaultSize() { return 32; }
+
  protected:
   std::unordered_map<DMatrix const*, Item> container_;
   std::queue<DMatrix const*> queue_;

include/xgboost/metric.h

@@ -54,12 +54,15 @@ class Metric : public Configurable {
     out["name"] = String(this->Name());
   }
 
-  /*!
-   * \brief evaluate a specific metric
-   * \param preds prediction
-   * \param info information, including label etc.
+  /**
+   * \brief Evaluate a metric with DMatrix as input.
+   *
+   * \param preds Prediction
+   * \param p_fmat DMatrix that contains related information like labels.
    */
-  virtual double Eval(const HostDeviceVector<bst_float>& preds, const MetaInfo& info) = 0;
+  virtual double Evaluate(HostDeviceVector<bst_float> const& preds,
+                          std::shared_ptr<DMatrix> p_fmat) = 0;
+
   /*! \return name of metric */
   virtual const char* Name() const = 0;
   /*! \brief virtual destructor */