Predict on Ellpack. (#5327)

* Unify GPU prediction node.
* Add `PageExists`.
* Dispatch prediction on input data for GPU Predictor.

include/xgboost/data.h

@@ -168,12 +168,19 @@ struct BatchParam {
   /*! \brief The GPU device to use. */
   int gpu_id;
   /*! \brief Maximum number of bins per feature for histograms. */
-  int max_bin;
+  int max_bin { 0 };
   /*! \brief Number of rows in a GPU batch, used for finding quantiles on GPU. */
   int gpu_batch_nrows;
   /*! \brief Page size for external memory mode. */
   size_t gpu_page_size;
-
+  BatchParam() = default;
+  BatchParam(int32_t device, int32_t max_bin, int32_t gpu_batch_nrows,
+             size_t gpu_page_size = 0) :
+      gpu_id{device},
+      max_bin{max_bin},
+      gpu_batch_nrows{gpu_batch_nrows},
+      gpu_page_size{gpu_page_size}
+  {}
   inline bool operator!=(const BatchParam& other) const {
     return gpu_id != other.gpu_id ||
         max_bin != other.max_bin ||
@@ -438,6 +445,9 @@ class DMatrix {
    */
   template<typename T>
   BatchSet<T> GetBatches(const BatchParam& param = {});
+  template <typename T>
+  bool PageExists() const;
+
   // the following are column meta data, should be able to answer them fast.
   /*! \return Whether the data columns single column block. */
   virtual bool SingleColBlock() const = 0;
@@ -493,6 +503,9 @@ class DMatrix {
   virtual BatchSet<CSCPage> GetColumnBatches() = 0;
   virtual BatchSet<SortedCSCPage> GetSortedColumnBatches() = 0;
   virtual BatchSet<EllpackPage> GetEllpackBatches(const BatchParam& param) = 0;
+
+  virtual bool EllpackExists() const = 0;
+  virtual bool SparsePageExists() const = 0;
 };
 
 template<>
@@ -500,6 +513,16 @@ inline BatchSet<SparsePage> DMatrix::GetBatches(const BatchParam&) {
   return GetRowBatches();
 }
 
+template<>
+inline bool DMatrix::PageExists<EllpackPage>() const {
+  return this->EllpackExists();
+}
+
+template<>
+inline bool DMatrix::PageExists<SparsePage>() const {
+  return this->SparsePageExists();
+}
+
 template<>
 inline BatchSet<CSCPage> DMatrix::GetBatches(const BatchParam&) {
   return GetColumnBatches();

include/xgboost/tree_model.h

@@ -105,7 +105,7 @@ class RegTree : public Model {
   /*! \brief tree node */
   class Node {
    public:
-    Node()  {
+    XGBOOST_DEVICE Node()  {
       // assert compact alignment
       static_assert(sizeof(Node) == 4 * sizeof(int) + sizeof(Info),
                     "Node: 64 bit align");
@@ -422,7 +422,7 @@ class RegTree : public Model {
      * \param i feature index.
      * \return the i-th feature value
      */
-    bst_float Fvalue(size_t i) const;
+    bst_float GetFvalue(size_t i) const;
     /*!
      * \brief check whether i-th entry is missing
      * \param i feature index.
@@ -565,7 +565,7 @@ inline size_t RegTree::FVec::Size() const {
   return data_.size();
 }
 
-inline bst_float RegTree::FVec::Fvalue(size_t i) const {
+inline bst_float RegTree::FVec::GetFvalue(size_t i) const {
   return data_[i].fvalue;
 }
 
@@ -577,7 +577,7 @@ inline int RegTree::GetLeafIndex(const RegTree::FVec& feat) const {
   bst_node_t nid = 0;
   while (!(*this)[nid].IsLeaf()) {
     unsigned split_index = (*this)[nid].SplitIndex();
-    nid = this->GetNext(nid, feat.Fvalue(split_index), feat.IsMissing(split_index));
+    nid = this->GetNext(nid, feat.GetFvalue(split_index), feat.IsMissing(split_index));
   }
   return nid;
 }