[EM] Enable access to the number of batches. (#10691)

- Expose `NumBatches` in `DMatrix`.
- Small cleanup for removing legacy CUDA stream and ~force CUDA context initialization~.
- Purge old external memory data generation code.

tests/cpp/predictor/test_cpu_predictor.cc

@@ -10,12 +10,10 @@
 #include "../../../src/gbm/gbtree.h"
 #include "../../../src/gbm/gbtree_model.h"
 #include "../collective/test_worker.h"  // for TestDistributedGlobal
-#include "../filesystem.h"  // dmlc::TemporaryDirectory
 #include "../helpers.h"
 #include "test_predictor.h"
 
 namespace xgboost {
-
 TEST(CpuPredictor, Basic) {
   Context ctx;
   size_t constexpr kRows = 5;
@@ -56,9 +54,10 @@ TEST(CpuPredictor, IterationRangeColmnSplit) {
 
 TEST(CpuPredictor, ExternalMemory) {
   Context ctx;
-  size_t constexpr kPageSize = 64, kEntriesPerCol = 3;
-  size_t constexpr kEntries = kPageSize * kEntriesPerCol * 2;
-  std::unique_ptr<DMatrix> dmat = CreateSparsePageDMatrix(kEntries);
+  bst_idx_t constexpr kRows{64};
+  bst_feature_t constexpr kCols{12};
+  auto dmat =
+      RandomDataGenerator{kRows, kCols, 0.5f}.Batches(3).GenerateSparsePageDMatrix("temp", true);
   TestBasic(dmat.get(), &ctx);
 }
 

tests/cpp/predictor/test_gpu_predictor.cu

@@ -123,8 +123,8 @@ TEST(GPUPredictor, EllpackBasic) {
     size_t rows = bins * 16;
     auto p_m = RandomDataGenerator{rows, kCols, 0.0}
                    .Bins(bins)
-                   .Device(DeviceOrd::CUDA(0))
-                   .GenerateDeviceDMatrix(false);
+                   .Device(ctx.Device())
+                   .GenerateQuantileDMatrix(false);
     ASSERT_FALSE(p_m->PageExists<SparsePage>());
     TestPredictionFromGradientIndex<EllpackPage>(&ctx, rows, kCols, p_m);
     TestPredictionFromGradientIndex<EllpackPage>(&ctx, bins, kCols, p_m);
@@ -137,7 +137,7 @@ TEST(GPUPredictor, EllpackTraining) {
   auto p_ellpack = RandomDataGenerator{kRows, kCols, 0.0}
                        .Bins(kBins)
                        .Device(ctx.Device())
-                       .GenerateDeviceDMatrix(false);
+                       .GenerateQuantileDMatrix(false);
   HostDeviceVector<float> storage(kRows * kCols);
   auto columnar =
       RandomDataGenerator{kRows, kCols, 0.0}.Device(ctx.Device()).GenerateArrayInterface(&storage);