Add data split mode to DMatrix MetaInfo

include/xgboost/data.h

@@ -60,6 +60,8 @@ class MetaInfo {
   uint64_t num_nonzero_{0};  // NOLINT
   /*! \brief label of each instance */
   linalg::Tensor<float, 2> labels;
+  /*! \brief data split mode */
+  DataSplitMode data_split_mode{DataSplitMode::kNone};
   /*!
    * \brief the index of begin and end of a group
    *  needed when the learning task is ranking.

src/data/simple_dmatrix.cc

@@ -65,6 +65,7 @@ DMatrix* SimpleDMatrix::SliceCol(std::size_t start, std::size_t size) {
     out->Info() = this->Info().Copy();
     out->Info().num_nonzero_ = h_offset.back();
   }
+  out->Info().data_split_mode = DataSplitMode::kCol;
   return out;
 }
 

tests/cpp/data/test_simple_dmatrix.cc

@@ -22,6 +22,7 @@ TEST(SimpleDMatrix, MetaInfo) {
   EXPECT_EQ(dmat->Info().num_col_, 5);
   EXPECT_EQ(dmat->Info().num_nonzero_, 6);
   EXPECT_EQ(dmat->Info().labels.Size(), dmat->Info().num_row_);
+  EXPECT_EQ(dmat->Info().data_split_mode, DataSplitMode::kNone);
 
   delete dmat;
 }
@@ -360,6 +361,7 @@ TEST(SimpleDMatrix, SliceCol) {
     ASSERT_EQ(out->Info().num_col_, out->Info().num_col_);
     ASSERT_EQ(out->Info().num_row_, kRows);
     ASSERT_EQ(out->Info().num_nonzero_, kRows * kSlicCols);  // dense
+    ASSERT_EQ(out->Info().data_split_mode, DataSplitMode::kCol);
   }
 }