[EM] Avoid writing cut matrix to cache. (#10444)

include/xgboost/data.h

@@ -113,7 +113,10 @@ class MetaInfo {
   MetaInfo Slice(common::Span<int32_t const> ridxs) const;
 
   MetaInfo Copy() const;
-
+  /**
+   * @brief Whether the matrix is dense.
+   */
+  bool IsDense() const { return num_col_ * num_row_ == num_nonzero_; }
   /*!
    * \brief Get weight of each instances.
    * \param i Instance index.
@@ -538,10 +541,10 @@ class DMatrix {
   /*! \brief virtual destructor */
   virtual ~DMatrix();
 
-  /*! \brief Whether the matrix is dense. */
+  /**
-  [[nodiscard]] bool IsDense() const {
+   * @brief Whether the matrix is dense.
-    return Info().num_nonzero_ == Info().num_row_ * Info().num_col_;
+   */
-  }
+  [[nodiscard]] bool IsDense() const { return this->Info().IsDense(); }
 
   /**
    * \brief Load DMatrix from URI.

src/collective/aggregator.h

@@ -9,7 +9,6 @@
 #include <limits>
 #include <string>
 #include <utility>
-#include <vector>
 
 #include "allreduce.h"
 #include "broadcast.h"

src/common/hist_util.h

@@ -162,6 +162,17 @@ class HistogramCuts {
     }
     return vals[bin_idx - 1];
   }
+
+  void SetDevice(DeviceOrd d) const {
+    this->cut_ptrs_.SetDevice(d);
+    this->cut_ptrs_.ConstDevicePointer();
+
+    this->cut_values_.SetDevice(d);
+    this->cut_values_.ConstDevicePointer();
+
+    this->min_vals_.SetDevice(d);
+    this->min_vals_.ConstDevicePointer();
+  }
 };
 
 /**

src/data/ellpack_page.cc

@@ -1,5 +1,5 @@
 /**
- * Copyright 2019-2023, XGBoost contributors
+ * Copyright 2019-2024, XGBoost contributors
  */
 #ifndef XGBOOST_USE_CUDA
 
@@ -7,15 +7,17 @@
 
 #include <xgboost/data.h>
 
+#include <memory>  // for shared_ptr
+
 // dummy implementation of EllpackPage in case CUDA is not used
 namespace xgboost {
 
 class EllpackPageImpl {
-  common::HistogramCuts cuts_;
+  std::shared_ptr<common::HistogramCuts> cuts_;
 
  public:
-  [[nodiscard]] common::HistogramCuts& Cuts() { return cuts_; }
+  [[nodiscard]] common::HistogramCuts const& Cuts() const { return *cuts_; }
-  [[nodiscard]] common::HistogramCuts const& Cuts() const { return cuts_; }
+  [[nodiscard]] std::shared_ptr<common::HistogramCuts const> CutsShared() const { return cuts_; }
 };
 
 EllpackPage::EllpackPage() = default;
@@ -40,12 +42,6 @@ size_t EllpackPage::Size() const {
   return 0;
 }
 
-[[nodiscard]] common::HistogramCuts& EllpackPage::Cuts() {
-  LOG(FATAL) << "Internal Error: XGBoost is not compiled with CUDA but "
-                "EllpackPage is required";
-  return impl_->Cuts();
-}
-
 [[nodiscard]] common::HistogramCuts const& EllpackPage::Cuts() const {
   LOG(FATAL) << "Internal Error: XGBoost is not compiled with CUDA but "
                 "EllpackPage is required";

src/data/ellpack_page.cu

@@ -12,8 +12,8 @@
 #include "../common/cuda_context.cuh"
 #include "../common/hist_util.cuh"
 #include "../common/transform_iterator.h"  // MakeIndexTransformIter
-#include "./ellpack_page.cuh"
+#include "device_adapter.cuh"              // for NoInfInData
-#include "device_adapter.cuh"  // for NoInfInData
+#include "ellpack_page.cuh"
 #include "ellpack_page.h"
 #include "gradient_index.h"
 #include "xgboost/data.h"
@@ -33,11 +33,6 @@ size_t EllpackPage::Size() const { return impl_->Size(); }
 
 void EllpackPage::SetBaseRowId(std::size_t row_id) { impl_->SetBaseRowId(row_id); }
 
-[[nodiscard]] common::HistogramCuts& EllpackPage::Cuts() {
-  CHECK(impl_);
-  return impl_->Cuts();
-}
-
 [[nodiscard]] common::HistogramCuts const& EllpackPage::Cuts() const {
   CHECK(impl_);
   return impl_->Cuts();
@@ -94,7 +89,8 @@ __global__ void CompressBinEllpackKernel(
 }
 
 // Construct an ELLPACK matrix with the given number of empty rows.
-EllpackPageImpl::EllpackPageImpl(DeviceOrd device, common::HistogramCuts cuts, bool is_dense,
+EllpackPageImpl::EllpackPageImpl(DeviceOrd device,
+                                 std::shared_ptr<common::HistogramCuts const> cuts, bool is_dense,
                                  size_t row_stride, size_t n_rows)
     : is_dense(is_dense), cuts_(std::move(cuts)), row_stride(row_stride), n_rows(n_rows) {
   monitor_.Init("ellpack_page");
@@ -105,12 +101,11 @@ EllpackPageImpl::EllpackPageImpl(DeviceOrd device, common::HistogramCuts cuts, b
   monitor_.Stop("InitCompressedData");
 }
 
-EllpackPageImpl::EllpackPageImpl(DeviceOrd device, common::HistogramCuts cuts,
+EllpackPageImpl::EllpackPageImpl(DeviceOrd device,
-                                 const SparsePage &page, bool is_dense,
+                                 std::shared_ptr<common::HistogramCuts const> cuts,
-                                 size_t row_stride,
+                                 const SparsePage& page, bool is_dense, size_t row_stride,
                                  common::Span<FeatureType const> feature_types)
-    : cuts_(std::move(cuts)), is_dense(is_dense), n_rows(page.Size()),
+    : cuts_(std::move(cuts)), is_dense(is_dense), n_rows(page.Size()), row_stride(row_stride) {
-      row_stride(row_stride) {
   this->InitCompressedData(device);
   this->CreateHistIndices(device, page, feature_types);
 }
@@ -127,9 +122,10 @@ EllpackPageImpl::EllpackPageImpl(Context const* ctx, DMatrix* dmat, const BatchP
   // Create the quantile sketches for the dmatrix and initialize HistogramCuts.
   row_stride = GetRowStride(dmat);
   if (!param.hess.empty()) {
-    cuts_ = common::DeviceSketchWithHessian(ctx, dmat, param.max_bin, param.hess);
+    cuts_ = std::make_shared<common::HistogramCuts>(
+        common::DeviceSketchWithHessian(ctx, dmat, param.max_bin, param.hess));
   } else {
-    cuts_ = common::DeviceSketch(ctx, dmat, param.max_bin);
+    cuts_ = std::make_shared<common::HistogramCuts>(common::DeviceSketch(ctx, dmat, param.max_bin));
   }
   monitor_.Stop("Quantiles");
 
@@ -297,7 +293,7 @@ template <typename AdapterBatch>
 EllpackPageImpl::EllpackPageImpl(AdapterBatch batch, float missing, DeviceOrd device, bool is_dense,
                                  common::Span<size_t> row_counts_span,
                                  common::Span<FeatureType const> feature_types, size_t row_stride,
-                                 size_t n_rows, common::HistogramCuts const& cuts) {
+                                 size_t n_rows, std::shared_ptr<common::HistogramCuts const> cuts) {
   dh::safe_cuda(cudaSetDevice(device.ordinal));
 
   *this = EllpackPageImpl(device, cuts, is_dense, row_stride, n_rows);
@@ -309,7 +305,7 @@ EllpackPageImpl::EllpackPageImpl(AdapterBatch batch, float missing, DeviceOrd de
   template EllpackPageImpl::EllpackPageImpl(                                               \
       __BATCH_T batch, float missing, DeviceOrd device, bool is_dense,                     \
       common::Span<size_t> row_counts_span, common::Span<FeatureType const> feature_types, \
-      size_t row_stride, size_t n_rows, common::HistogramCuts const& cuts);
+      size_t row_stride, size_t n_rows, std::shared_ptr<common::HistogramCuts const> cuts);
 
 ELLPACK_BATCH_SPECIALIZE(data::CudfAdapterBatch)
 ELLPACK_BATCH_SPECIALIZE(data::CupyAdapterBatch)
@@ -359,7 +355,11 @@ void CopyGHistToEllpack(GHistIndexMatrix const& page, common::Span<size_t const>
 
 EllpackPageImpl::EllpackPageImpl(Context const* ctx, GHistIndexMatrix const& page,
                                  common::Span<FeatureType const> ft)
-    : is_dense{page.IsDense()}, base_rowid{page.base_rowid}, n_rows{page.Size()}, cuts_{page.cut} {
+    : is_dense{page.IsDense()},
+      base_rowid{page.base_rowid},
+      n_rows{page.Size()},
+      // This makes a copy of the cut values.
+      cuts_{std::make_shared<common::HistogramCuts>(page.cut)} {
   auto it = common::MakeIndexTransformIter(
       [&](size_t i) { return page.row_ptr[i + 1] - page.row_ptr[i]; });
   row_stride = *std::max_element(it, it + page.Size());

src/data/ellpack_page.cuh

@@ -23,20 +23,20 @@ struct EllpackDeviceAccessor {
   bool is_dense;
   /*! \brief Row length for ELLPACK, equal to number of features. */
   size_t row_stride;
-  size_t base_rowid{};
+  bst_idx_t base_rowid{0};
-  size_t n_rows{};
+  bst_idx_t n_rows{0};
-  common::CompressedIterator<uint32_t> gidx_iter;
+  common::CompressedIterator<std::uint32_t> gidx_iter;
   /*! \brief Minimum value for each feature. Size equals to number of features. */
-  common::Span<const bst_float> min_fvalue;
+  common::Span<const float> min_fvalue;
   /*! \brief Histogram cut pointers. Size equals to (number of features + 1). */
-  common::Span<const uint32_t> feature_segments;
+  common::Span<const std::uint32_t> feature_segments;
   /*! \brief Histogram cut values. Size equals to (bins per feature * number of features). */
-  common::Span<const bst_float> gidx_fvalue_map;
+  common::Span<const float> gidx_fvalue_map;
 
   common::Span<const FeatureType> feature_types;
 
-  EllpackDeviceAccessor(DeviceOrd device, const common::HistogramCuts& cuts, bool is_dense,
+  EllpackDeviceAccessor(DeviceOrd device, std::shared_ptr<const common::HistogramCuts> cuts,
-                        size_t row_stride, size_t base_rowid, size_t n_rows,
+                        bool is_dense, size_t row_stride, size_t base_rowid, size_t n_rows,
                         common::CompressedIterator<uint32_t> gidx_iter,
                         common::Span<FeatureType const> feature_types)
       : is_dense(is_dense),
@@ -46,16 +46,16 @@ struct EllpackDeviceAccessor {
         gidx_iter(gidx_iter),
         feature_types{feature_types} {
     if (device.IsCPU()) {
-      gidx_fvalue_map = cuts.cut_values_.ConstHostSpan();
+      gidx_fvalue_map = cuts->cut_values_.ConstHostSpan();
-      feature_segments = cuts.cut_ptrs_.ConstHostSpan();
+      feature_segments = cuts->cut_ptrs_.ConstHostSpan();
-      min_fvalue = cuts.min_vals_.ConstHostSpan();
+      min_fvalue = cuts->min_vals_.ConstHostSpan();
     } else {
-      cuts.cut_values_.SetDevice(device);
+      cuts->cut_values_.SetDevice(device);
-      cuts.cut_ptrs_.SetDevice(device);
+      cuts->cut_ptrs_.SetDevice(device);
-      cuts.min_vals_.SetDevice(device);
+      cuts->min_vals_.SetDevice(device);
-      gidx_fvalue_map = cuts.cut_values_.ConstDeviceSpan();
+      gidx_fvalue_map = cuts->cut_values_.ConstDeviceSpan();
-      feature_segments = cuts.cut_ptrs_.ConstDeviceSpan();
+      feature_segments = cuts->cut_ptrs_.ConstDeviceSpan();
-      min_fvalue = cuts.min_vals_.ConstDeviceSpan();
+      min_fvalue = cuts->min_vals_.ConstDeviceSpan();
     }
   }
   // Get a matrix element, uses binary search for look up Return NaN if missing
@@ -142,13 +142,14 @@ class EllpackPageImpl {
    * This is used in the sampling case. The ELLPACK page is constructed from an existing EllpackInfo
    * and the given number of rows.
    */
-  EllpackPageImpl(DeviceOrd device, common::HistogramCuts cuts, bool is_dense, size_t row_stride,
+  EllpackPageImpl(DeviceOrd device, std::shared_ptr<common::HistogramCuts const> cuts,
-                  size_t n_rows);
+                  bool is_dense, size_t row_stride, size_t n_rows);
   /*!
    * \brief Constructor used for external memory.
    */
-  EllpackPageImpl(DeviceOrd device, common::HistogramCuts cuts, const SparsePage& page,
+  EllpackPageImpl(DeviceOrd device, std::shared_ptr<common::HistogramCuts const> cuts,
-                  bool is_dense, size_t row_stride, common::Span<FeatureType const> feature_types);
+                  const SparsePage& page, bool is_dense, size_t row_stride,
+                  common::Span<FeatureType const> feature_types);
 
   /*!
    * \brief Constructor from an existing DMatrix.
@@ -162,7 +163,7 @@ class EllpackPageImpl {
   explicit EllpackPageImpl(AdapterBatch batch, float missing, DeviceOrd device, bool is_dense,
                            common::Span<size_t> row_counts_span,
                            common::Span<FeatureType const> feature_types, size_t row_stride,
-                           size_t n_rows, common::HistogramCuts const& cuts);
+                           size_t n_rows, std::shared_ptr<common::HistogramCuts const> cuts);
   /**
    * \brief Constructor from an existing CPU gradient index.
    */
@@ -194,8 +195,9 @@ class EllpackPageImpl {
     base_rowid = row_id;
   }
 
-  [[nodiscard]] common::HistogramCuts& Cuts() { return cuts_; }
+  [[nodiscard]] common::HistogramCuts const& Cuts() const { return *cuts_; }
-  [[nodiscard]] common::HistogramCuts const& Cuts() const { return cuts_; }
+  [[nodiscard]] std::shared_ptr<common::HistogramCuts const> CutsShared() const { return cuts_; }
+  void SetCuts(std::shared_ptr<common::HistogramCuts const> cuts) { cuts_ = cuts; }
 
   /*! \return Estimation of memory cost of this page. */
   static size_t MemCostBytes(size_t num_rows, size_t row_stride, const common::HistogramCuts&cuts) ;
@@ -203,7 +205,7 @@ class EllpackPageImpl {
 
   /*! \brief Return the total number of symbols (total number of bins plus 1 for
    * not found). */
-  [[nodiscard]] std::size_t NumSymbols() const { return cuts_.TotalBins() + 1; }
+  [[nodiscard]] std::size_t NumSymbols() const { return cuts_->TotalBins() + 1; }
 
   [[nodiscard]] EllpackDeviceAccessor GetDeviceAccessor(
       DeviceOrd device, common::Span<FeatureType const> feature_types = {}) const;
@@ -225,19 +227,18 @@ class EllpackPageImpl {
    */
   void InitCompressedData(DeviceOrd device);
 
-
+ public:
-public:
   /*! \brief Whether or not if the matrix is dense. */
   bool is_dense;
   /*! \brief Row length for ELLPACK. */
   size_t row_stride;
-  size_t base_rowid{0};
+  bst_idx_t base_rowid{0};
-  size_t n_rows{};
+  bst_idx_t n_rows{};
   /*! \brief global index of histogram, which is stored in ELLPACK format. */
   HostDeviceVector<common::CompressedByteT> gidx_buffer;
 
  private:
-  common::HistogramCuts cuts_;
+  std::shared_ptr<common::HistogramCuts const> cuts_;
   common::Monitor monitor_;
 };
 

src/data/ellpack_page.h

@@ -49,7 +49,6 @@ class EllpackPage {
   [[nodiscard]] const EllpackPageImpl* Impl() const { return impl_.get(); }
   EllpackPageImpl* Impl() { return impl_.get(); }
 
-  [[nodiscard]] common::HistogramCuts& Cuts();
   [[nodiscard]] common::HistogramCuts const& Cuts() const;
 
  private:

src/data/ellpack_page_raw_format.cu

@@ -1,60 +1,78 @@
 /**
- * Copyright 2019-2023, XGBoost contributors
+ * Copyright 2019-2024, XGBoost contributors
  */
 #include <dmlc/registry.h>
 
 #include <cstddef>  // for size_t
+#include <cstdint>  // for uint64_t
 
 #include "../common/io.h"                 // for AlignedResourceReadStream, AlignedFileWriteStream
 #include "../common/ref_resource_view.h"  // for ReadVec, WriteVec
-#include "ellpack_page.cuh"
+#include "ellpack_page.cuh"               // for EllpackPage
-#include "histogram_cut_format.h"  // for ReadHistogramCuts, WriteHistogramCuts
+#include "ellpack_page_raw_format.h"
-#include "sparse_page_writer.h"    // for SparsePageFormat
 
 namespace xgboost::data {
 DMLC_REGISTRY_FILE_TAG(ellpack_page_raw_format);
 
-class EllpackPageRawFormat : public SparsePageFormat<EllpackPage> {
+namespace {
- public:
+template <typename T>
-  bool Read(EllpackPage* page, common::AlignedResourceReadStream* fi) override {
+[[nodiscard]] bool ReadDeviceVec(common::AlignedResourceReadStream* fi, HostDeviceVector<T>* vec) {
-    auto* impl = page->Impl();
+  std::uint64_t n{0};
-    if (!ReadHistogramCuts(&impl->Cuts(), fi)) {
+  if (!fi->Read(&n)) {
-      return false;
+    return false;
-    }
+  }
-    if (!fi->Read(&impl->n_rows)) {
+  if (n == 0) {
-      return false;
-    }
-    if (!fi->Read(&impl->is_dense)) {
-      return false;
-    }
-    if (!fi->Read(&impl->row_stride)) {
-      return false;
-    }
-    if (!common::ReadVec(fi, &impl->gidx_buffer.HostVector())) {
-      return false;
-    }
-    if (!fi->Read(&impl->base_rowid)) {
-      return false;
-    }
-    dh::DefaultStream().Sync();
     return true;
   }
 
-  size_t Write(const EllpackPage& page, common::AlignedFileWriteStream* fo) override {
+  auto expected_bytes = sizeof(T) * n;
-    std::size_t bytes{0};
-    auto* impl = page.Impl();
-    bytes += WriteHistogramCuts(impl->Cuts(), fo);
-    bytes += fo->Write(impl->n_rows);
-    bytes += fo->Write(impl->is_dense);
-    bytes += fo->Write(impl->row_stride);
-    CHECK(!impl->gidx_buffer.ConstHostVector().empty());
-    bytes += common::WriteVec(fo, impl->gidx_buffer.HostVector());
-    bytes += fo->Write(impl->base_rowid);
-    return bytes;
-  }
-};
 
-XGBOOST_REGISTER_ELLPACK_PAGE_FORMAT(raw)
+  auto [ptr, n_bytes] = fi->Consume(expected_bytes);
-    .describe("Raw ELLPACK binary data format.")
+  if (n_bytes != expected_bytes) {
-    .set_body([]() { return new EllpackPageRawFormat(); });
+    return false;
+  }
+
+  vec->SetDevice(DeviceOrd::CUDA(0));
+  vec->Resize(n);
+  auto d_vec = vec->DeviceSpan();
+  dh::safe_cuda(
+      cudaMemcpyAsync(d_vec.data(), ptr, n_bytes, cudaMemcpyDefault, dh::DefaultStream()));
+  return true;
+}
+}  // namespace
+
+[[nodiscard]] bool EllpackPageRawFormat::Read(EllpackPage* page,
+                                              common::AlignedResourceReadStream* fi) {
+  auto* impl = page->Impl();
+  impl->SetCuts(this->cuts_);
+  if (!fi->Read(&impl->n_rows)) {
+    return false;
+  }
+  if (!fi->Read(&impl->is_dense)) {
+    return false;
+  }
+  if (!fi->Read(&impl->row_stride)) {
+    return false;
+  }
+  if (!ReadDeviceVec(fi, &impl->gidx_buffer)) {
+    return false;
+  }
+  if (!fi->Read(&impl->base_rowid)) {
+    return false;
+  }
+  return true;
+}
+
+[[nodiscard]] std::size_t EllpackPageRawFormat::Write(const EllpackPage& page,
+                                                      common::AlignedFileWriteStream* fo) {
+  std::size_t bytes{0};
+  auto* impl = page.Impl();
+  bytes += fo->Write(impl->n_rows);
+  bytes += fo->Write(impl->is_dense);
+  bytes += fo->Write(impl->row_stride);
+  CHECK(!impl->gidx_buffer.ConstHostVector().empty());
+  bytes += common::WriteVec(fo, impl->gidx_buffer.HostVector());
+  bytes += fo->Write(impl->base_rowid);
+  return bytes;
+}
 }  // namespace xgboost::data

src/data/ellpack_page_raw_format.h

@@ -0,0 +1,46 @@
+/**
+ * Copyright 2019-2024, XGBoost contributors
+ */
+#pragma once
+
+#include <cstddef>  // for size_t
+#include <memory>   // for shared_ptr
+#include <utility>  // for move
+
+#include "../common/io.h"        // for AlignedResourceReadStream
+#include "sparse_page_writer.h"  // for SparsePageFormat
+#include "xgboost/data.h"        // for EllpackPage
+
+#if !defined(XGBOOST_USE_CUDA)
+#include "../common/common.h"  // for AssertGPUSupport
+#endif                         // !defined(XGBOOST_USE_CUDA)`
+
+namespace xgboost::common {
+class HistogramCuts;
+}
+
+namespace xgboost::data {
+class EllpackPageRawFormat : public SparsePageFormat<EllpackPage> {
+  std::shared_ptr<common::HistogramCuts const> cuts_;
+
+ public:
+  explicit EllpackPageRawFormat(std::shared_ptr<common::HistogramCuts const> cuts)
+      : cuts_{std::move(cuts)} {}
+  [[nodiscard]] bool Read(EllpackPage* page, common::AlignedResourceReadStream* fi) override;
+  [[nodiscard]] std::size_t Write(const EllpackPage& page,
+                                  common::AlignedFileWriteStream* fo) override;
+};
+
+#if !defined(XGBOOST_USE_CUDA)
+inline bool EllpackPageRawFormat::Read(EllpackPage*, common::AlignedResourceReadStream*) {
+  common::AssertGPUSupport();
+  return false;
+}
+
+inline std::size_t EllpackPageRawFormat::Write(const EllpackPage&,
+                                               common::AlignedFileWriteStream*) {
+  common::AssertGPUSupport();
+  return 0;
+}
+#endif  // !defined(XGBOOST_USE_CUDA)
+}  // namespace xgboost::data

src/data/ellpack_page_source.cu

@@ -21,7 +21,7 @@ void EllpackPageSource::Fetch() {
     auto const &csr = source_->Page();
     this->page_.reset(new EllpackPage{});
     auto *impl = this->page_->Impl();
-    *impl = EllpackPageImpl(device_, *cuts_, *csr, is_dense_, row_stride_, feature_types_);
+    *impl = EllpackPageImpl(device_, cuts_, *csr, is_dense_, row_stride_, feature_types_);
     page_->SetBaseRowId(csr->base_rowid);
     this->WriteCache();
   }

src/data/ellpack_page_source.h

@@ -1,35 +1,43 @@
 /**
- * Copyright 2019-2023, XGBoost Contributors
+ * Copyright 2019-2024, XGBoost Contributors
  */
 
 #ifndef XGBOOST_DATA_ELLPACK_PAGE_SOURCE_H_
 #define XGBOOST_DATA_ELLPACK_PAGE_SOURCE_H_
 
-#include <xgboost/data.h>
+#include <cstdint>  // for int32_t
+#include <memory>   // for shared_ptr
+#include <utility>  // for move
 
-#include <memory>
+#include "../common/hist_util.h"      // for HistogramCuts
-#include <string>
+#include "ellpack_page.h"             // for EllpackPage
-#include <utility>
+#include "ellpack_page_raw_format.h"  // for EllpackPageRawFormat
-
+#include "sparse_page_source.h"       // for PageSourceIncMixIn
-#include "../common/common.h"
+#include "xgboost/base.h"             // for bst_idx_t
-#include "../common/hist_util.h"
+#include "xgboost/context.h"          // for DeviceOrd
-#include "ellpack_page.h"  // for EllpackPage
+#include "xgboost/data.h"             // for BatchParam
-#include "sparse_page_source.h"
+#include "xgboost/span.h"             // for Span
 
 namespace xgboost::data {
 class EllpackPageSource : public PageSourceIncMixIn<EllpackPage> {
   bool is_dense_;
-  size_t row_stride_;
+  bst_idx_t row_stride_;
   BatchParam param_;
   common::Span<FeatureType const> feature_types_;
-  std::unique_ptr<common::HistogramCuts> cuts_;
+  std::shared_ptr<common::HistogramCuts const> cuts_;
   DeviceOrd device_;
 
+ protected:
+  [[nodiscard]] SparsePageFormat<EllpackPage>* CreatePageFormat() const override {
+    cuts_->SetDevice(this->device_);
+    return new EllpackPageRawFormat{cuts_};
+  }
+
  public:
-  EllpackPageSource(float missing, int nthreads, bst_feature_t n_features, size_t n_batches,
+  EllpackPageSource(float missing, std::int32_t nthreads, bst_feature_t n_features,
-                    std::shared_ptr<Cache> cache, BatchParam param,
+                    size_t n_batches, std::shared_ptr<Cache> cache, BatchParam param,
-                    std::unique_ptr<common::HistogramCuts> cuts, bool is_dense, size_t row_stride,
+                    std::shared_ptr<common::HistogramCuts const> cuts, bool is_dense,
-                    common::Span<FeatureType const> feature_types,
+                    bst_idx_t row_stride, common::Span<FeatureType const> feature_types,
                     std::shared_ptr<SparsePageSource> source, DeviceOrd device)
       : PageSourceIncMixIn(missing, nthreads, n_features, n_batches, cache, false),
         is_dense_{is_dense},

src/data/gradient_index_format.cc

@@ -1,106 +1,97 @@
 /**
- * Copyright 2021-2024 XGBoost contributors
+ * Copyright 2021-2024, XGBoost contributors
  */
-#include <cstddef>      // for size_t
+#include "gradient_index_format.h"
-#include <cstdint>      // for uint8_t
-#include <type_traits>  // for underlying_type_t
-#include <vector>       // for vector
 
+#include <cstddef>                        // for size_t
+#include <cstdint>                        // for uint8_t
+#include <type_traits>                    // for underlying_type_t
+#include <vector>                         // for vector
+
+#include "../common/hist_util.h"          // for HistogramCuts
 #include "../common/io.h"                 // for AlignedResourceReadStream
 #include "../common/ref_resource_view.h"  // for ReadVec, WriteVec
 #include "gradient_index.h"               // for GHistIndexMatrix
-#include "histogram_cut_format.h"         // for ReadHistogramCuts
-#include "sparse_page_writer.h"           // for SparsePageFormat
 
 namespace xgboost::data {
-class GHistIndexRawFormat : public SparsePageFormat<GHistIndexMatrix> {
+[[nodiscard]] bool GHistIndexRawFormat::Read(GHistIndexMatrix* page,
- public:
+                                             common::AlignedResourceReadStream* fi) {
-  bool Read(GHistIndexMatrix* page, common::AlignedResourceReadStream* fi) override {
+  CHECK(fi);
-    CHECK(fi);
 
-    if (!ReadHistogramCuts(&page->cut, fi)) {
+  page->Cuts() = this->cuts_;
-      return false;
+  // indptr
-    }
+  if (!common::ReadVec(fi, &page->row_ptr)) {
-
+    return false;
-    // indptr
-    if (!common::ReadVec(fi, &page->row_ptr)) {
-      return false;
-    }
-
-    // data
-    // - bin type
-    // Old gcc doesn't support reading from enum.
-    std::underlying_type_t<common::BinTypeSize> uint_bin_type{0};
-    if (!fi->Read(&uint_bin_type)) {
-      return false;
-    }
-    common::BinTypeSize size_type = static_cast<common::BinTypeSize>(uint_bin_type);
-    // - index buffer
-    if (!common::ReadVec(fi, &page->data)) {
-      return false;
-    }
-    // - index
-    page->index =
-        common::Index{common::Span{page->data.data(), static_cast<size_t>(page->data.size())},
-            size_type};
-
-    // hit count
-    if (!common::ReadVec(fi, &page->hit_count)) {
-      return false;
-    }
-    if (!fi->Read(&page->max_numeric_bins_per_feat)) {
-      return false;
-    }
-    if (!fi->Read(&page->base_rowid)) {
-      return false;
-    }
-    bool is_dense = false;
-    if (!fi->Read(&is_dense)) {
-      return false;
-    }
-    page->SetDense(is_dense);
-    if (is_dense) {
-      page->index.SetBinOffset(page->cut.Ptrs());
-    }
-
-    if (!page->ReadColumnPage(fi)) {
-      return false;
-    }
-    return true;
   }
 
-  std::size_t Write(GHistIndexMatrix const& page, common::AlignedFileWriteStream* fo) override {
+  // data
-    std::size_t bytes = 0;
+  // - bin type
-    bytes += WriteHistogramCuts(page.cut, fo);
+  // Old gcc doesn't support reading from enum.
-    // indptr
+  std::underlying_type_t<common::BinTypeSize> uint_bin_type{0};
-    bytes += common::WriteVec(fo, page.row_ptr);
+  if (!fi->Read(&uint_bin_type)) {
-
+    return false;
-    // data
-    // - bin type
-    std::underlying_type_t<common::BinTypeSize> uint_bin_type = page.index.GetBinTypeSize();
-    bytes += fo->Write(uint_bin_type);
-    // - index buffer
-    std::vector<std::uint8_t> data(page.index.begin(), page.index.end());
-    bytes += fo->Write(static_cast<std::uint64_t>(data.size()));
-    if (!data.empty()) {
-      bytes += fo->Write(data.data(), data.size());
-    }
-
-    // hit count
-    bytes += common::WriteVec(fo, page.hit_count);
-    // max_bins, base row, is_dense
-    bytes += fo->Write(page.max_numeric_bins_per_feat);
-    bytes += fo->Write(page.base_rowid);
-    bytes += fo->Write(page.IsDense());
-
-    bytes += page.WriteColumnPage(fo);
-    return bytes;
   }
-};
+  common::BinTypeSize size_type = static_cast<common::BinTypeSize>(uint_bin_type);
+  // - index buffer
+  if (!common::ReadVec(fi, &page->data)) {
+    return false;
+  }
+  // - index
+  page->index = common::Index{
+      common::Span{page->data.data(), static_cast<size_t>(page->data.size())}, size_type};
+
+  // hit count
+  if (!common::ReadVec(fi, &page->hit_count)) {
+    return false;
+  }
+  if (!fi->Read(&page->max_numeric_bins_per_feat)) {
+    return false;
+  }
+  if (!fi->Read(&page->base_rowid)) {
+    return false;
+  }
+  bool is_dense = false;
+  if (!fi->Read(&is_dense)) {
+    return false;
+  }
+  page->SetDense(is_dense);
+  if (is_dense) {
+    page->index.SetBinOffset(page->cut.Ptrs());
+  }
+
+  if (!page->ReadColumnPage(fi)) {
+    return false;
+  }
+  return true;
+}
+
+[[nodiscard]] std::size_t GHistIndexRawFormat::Write(GHistIndexMatrix const& page,
+                                                     common::AlignedFileWriteStream* fo) {
+  std::size_t bytes = 0;
+  // indptr
+  bytes += common::WriteVec(fo, page.row_ptr);
+
+  // data
+  // - bin type
+  std::underlying_type_t<common::BinTypeSize> uint_bin_type = page.index.GetBinTypeSize();
+  bytes += fo->Write(uint_bin_type);
+  // - index buffer
+  std::vector<std::uint8_t> data(page.index.begin(), page.index.end());
+  bytes += fo->Write(static_cast<std::uint64_t>(data.size()));
+  if (!data.empty()) {
+    bytes += fo->Write(data.data(), data.size());
+  }
+
+  // hit count
+  bytes += common::WriteVec(fo, page.hit_count);
+  // max_bins, base row, is_dense
+  bytes += fo->Write(page.max_numeric_bins_per_feat);
+  bytes += fo->Write(page.base_rowid);
+  bytes += fo->Write(page.IsDense());
+
+  bytes += page.WriteColumnPage(fo);
+  return bytes;
+}
 
 DMLC_REGISTRY_FILE_TAG(gradient_index_format);
-
-XGBOOST_REGISTER_GHIST_INDEX_PAGE_FORMAT(raw)
-    .describe("Raw GHistIndex binary data format.")
-    .set_body([]() { return new GHistIndexRawFormat(); });
 }  // namespace xgboost::data

src/data/gradient_index_format.h

@@ -0,0 +1,29 @@
+/**
+ * Copyright 2021-2024, XGBoost contributors
+ */
+#pragma once
+
+#include <cstddef>  // for size_t
+#include <utility>  // for move
+
+#include "../common/hist_util.h"  // for HistogramCuts
+#include "../common/io.h"         // for AlignedFileWriteStream
+#include "gradient_index.h"       // for GHistIndexMatrix
+#include "sparse_page_writer.h"   // for SparsePageFormat
+
+namespace xgboost::common {
+class HistogramCuts;
+}
+
+namespace xgboost::data {
+class GHistIndexRawFormat : public SparsePageFormat<GHistIndexMatrix> {
+  common::HistogramCuts cuts_;
+
+ public:
+  [[nodiscard]] bool Read(GHistIndexMatrix* page, common::AlignedResourceReadStream* fi) override;
+  [[nodiscard]] std::size_t Write(GHistIndexMatrix const& page,
+                                  common::AlignedFileWriteStream* fo) override;
+
+  explicit GHistIndexRawFormat(common::HistogramCuts cuts) : cuts_{std::move(cuts)} {}
+};
+}  // namespace xgboost::data

src/data/gradient_index_page_source.cc

@@ -1,5 +1,5 @@
 /**
- * Copyright 2021-2023, XGBoost Contributors
+ * Copyright 2021-2024, XGBoost Contributors
  */
 #include "gradient_index_page_source.h"
 

src/data/gradient_index_page_source.h

@@ -1,27 +1,39 @@
-/*!
+/**
- * Copyright 2021-2022 by XGBoost Contributors
+ * Copyright 2021-2024, XGBoost Contributors
  */
 #ifndef XGBOOST_DATA_GRADIENT_INDEX_PAGE_SOURCE_H_
 #define XGBOOST_DATA_GRADIENT_INDEX_PAGE_SOURCE_H_
 
-#include <memory>
+#include <cmath>    // for isnan
-#include <utility>
+#include <cstdint>  // for int32_t
+#include <memory>   // for shared_ptr
+#include <utility>  // for move
 
-#include "gradient_index.h"
+#include "../common/hist_util.h"    // for HistogramCuts
-#include "sparse_page_source.h"
+#include "gradient_index.h"         // for GHistIndexMatrix
+#include "gradient_index_format.h"  // for GHistIndexRawFormat
+#include "sparse_page_source.h"     // for PageSourceIncMixIn
+#include "xgboost/base.h"           // for bst_feature_t
+#include "xgboost/data.h"           // for BatchParam, FeatureType
+#include "xgboost/span.h"           // for Span
 
 namespace xgboost {
 namespace data {
 class GradientIndexPageSource : public PageSourceIncMixIn<GHistIndexMatrix> {
   common::HistogramCuts cuts_;
   bool is_dense_;
-  int32_t max_bin_per_feat_;
+  std::int32_t max_bin_per_feat_;
   common::Span<FeatureType const> feature_types_;
   double sparse_thresh_;
 
+ protected:
+  [[nodiscard]] SparsePageFormat<GHistIndexMatrix>* CreatePageFormat() const override {
+    return new GHistIndexRawFormat{cuts_};
+  }
+
  public:
-  GradientIndexPageSource(float missing, int nthreads, bst_feature_t n_features, size_t n_batches,
+  GradientIndexPageSource(float missing, std::int32_t nthreads, bst_feature_t n_features,
-                          std::shared_ptr<Cache> cache, BatchParam param,
+                          size_t n_batches, std::shared_ptr<Cache> cache, BatchParam param,
                           common::HistogramCuts cuts, bool is_dense,
                           common::Span<FeatureType const> feature_types,
                           std::shared_ptr<SparsePageSource> source)

src/data/iterative_dmatrix.cu

@@ -54,7 +54,7 @@ void IterativeDMatrix::InitFromCUDA(Context const* ctx, BatchParam const& p,
   /**
    * Generate quantiles
    */
-  common::HistogramCuts cuts;
+  auto cuts = std::make_shared<common::HistogramCuts>();
   do {
     // We use do while here as the first batch is fetched in ctor
     CHECK_LT(ctx->Ordinal(), common::AllVisibleGPUs());
@@ -104,9 +104,9 @@ void IterativeDMatrix::InitFromCUDA(Context const* ctx, BatchParam const& p,
     sketch_containers.clear();
     sketch_containers.shrink_to_fit();
 
-    final_sketch.MakeCuts(ctx, &cuts, this->info_.IsColumnSplit());
+    final_sketch.MakeCuts(ctx, cuts.get(), this->info_.IsColumnSplit());
   } else {
-    GetCutsFromRef(ctx, ref, Info().num_col_, p, &cuts);
+    GetCutsFromRef(ctx, ref, Info().num_col_, p, cuts.get());
   }
 
   this->info_.num_row_ = accumulated_rows;

src/data/sparse_page_dmatrix.cu

@@ -1,7 +1,7 @@
 /**
  * Copyright 2021-2024, XGBoost contributors
  */
-#include <memory>  // for unique_ptr
+#include <memory>  // for shared_ptr
 
 #include "../common/hist_util.cuh"
 #include "../common/hist_util.h"  // for HistogramCuts
@@ -26,13 +26,13 @@ BatchSet<EllpackPage> SparsePageDMatrix::GetEllpackBatches(Context const* ctx,
     // reinitialize the cache
     cache_info_.erase(id);
     MakeCache(this, ".ellpack.page", cache_prefix_, &cache_info_);
-    std::unique_ptr<common::HistogramCuts> cuts;
+    std::shared_ptr<common::HistogramCuts> cuts;
     if (!param.hess.empty()) {
-      cuts = std::make_unique<common::HistogramCuts>(
+      cuts = std::make_shared<common::HistogramCuts>(
           common::DeviceSketchWithHessian(ctx, this, param.max_bin, param.hess));
     } else {
       cuts =
-          std::make_unique<common::HistogramCuts>(common::DeviceSketch(ctx, this, param.max_bin));
+          std::make_shared<common::HistogramCuts>(common::DeviceSketch(ctx, this, param.max_bin));
     }
     this->InitializeSparsePage(ctx);  // reset after use.
 

src/data/sparse_page_source.h

@@ -7,6 +7,7 @@
 
 #include <algorithm>  // for min
 #include <atomic>     // for atomic
+#include <cstdint>    // for uint64_t
 #include <cstdio>     // for remove
 #include <future>     // for future
 #include <memory>     // for unique_ptr
@@ -72,9 +73,13 @@ struct Cache {
    */
   [[nodiscard]] auto View(std::size_t i) const {
     std::uint64_t off = offset.at(i);
-    std::uint64_t len = offset.at(i + 1) - offset[i];
+    std::uint64_t len = this->Bytes(i);
     return std::pair{off, len};
   }
+  /**
+   * @brief Get the number of bytes for the i^th page.
+   */
+  [[nodiscard]] std::uint64_t Bytes(std::size_t i) const { return offset.at(i + 1) - offset[i]; }
   /**
    * @brief Call this once the write for the cache is complete.
    */
@@ -174,6 +179,10 @@ class SparsePageSourceImpl : public BatchIteratorImpl<S> {
   ExceHandler exce_;
   common::Monitor monitor_;
 
+  [[nodiscard]] virtual SparsePageFormat<S>* CreatePageFormat() const {
+    return ::xgboost::data::CreatePageFormat<S>("raw");
+  }
+
   [[nodiscard]] bool ReadCache() {
     CHECK(!at_end_);
     if (!cache_info_->written) {
@@ -207,7 +216,7 @@ class SparsePageSourceImpl : public BatchIteratorImpl<S> {
         *GlobalConfigThreadLocalStore::Get() = config;
         auto page = std::make_shared<S>();
         this->exce_.Run([&] {
-          std::unique_ptr<SparsePageFormat<S>> fmt{CreatePageFormat<S>("raw")};
+          std::unique_ptr<SparsePageFormat<S>> fmt{this->CreatePageFormat()};
           auto name = self->cache_info_->ShardName();
           auto [offset, length] = self->cache_info_->View(fetch_it);
           auto fi = std::make_unique<common::PrivateMmapConstStream>(name, offset, length);
@@ -234,7 +243,7 @@ class SparsePageSourceImpl : public BatchIteratorImpl<S> {
     CHECK(!cache_info_->written);
     common::Timer timer;
     timer.Start();
-    std::unique_ptr<SparsePageFormat<S>> fmt{CreatePageFormat<S>("raw")};
+    std::unique_ptr<SparsePageFormat<S>> fmt{this->CreatePageFormat()};
 
     auto name = cache_info_->ShardName();
     std::unique_ptr<common::AlignedFileWriteStream> fo;
@@ -404,8 +413,8 @@ class PageSourceIncMixIn : public SparsePageSourceImpl<S> {
   bool sync_{true};
 
  public:
-  PageSourceIncMixIn(float missing, int nthreads, bst_feature_t n_features, std::uint32_t n_batches,
+  PageSourceIncMixIn(float missing, std::int32_t nthreads, bst_feature_t n_features,
-                     std::shared_ptr<Cache> cache, bool sync)
+                     std::uint32_t n_batches, std::shared_ptr<Cache> cache, bool sync)
       : Super::SparsePageSourceImpl{missing, nthreads, n_features, n_batches, cache}, sync_{sync} {}
 
   [[nodiscard]] PageSourceIncMixIn& operator++() final {

src/data/sparse_page_writer.h

@@ -10,7 +10,6 @@
 #include <string>      // for string
 
 #include "../common/io.h"   // for AlignedResourceReadStream, AlignedFileWriteStream
-#include "dmlc/io.h"        // for Stream
 #include "dmlc/registry.h"  // for Registry, FunctionRegEntryBase
 #include "xgboost/data.h"   // for SparsePage,CSCPage,SortedCSCPage,EllpackPage ...
 

src/global_config.cc

@@ -7,7 +7,6 @@
 
 #include <dmlc/thread_local.h>
 #include "xgboost/global_config.h"
-#include "xgboost/json.h"
 
 namespace xgboost {
 DMLC_REGISTER_PARAMETER(GlobalConfiguration);

src/tree/gpu_hist/feature_groups.cuh

@@ -1,5 +1,5 @@
 /**
- * Copyright 2020-2023 by XGBoost Contributors
+ * Copyright 2020-2024, XGBoost Contributors
  */
 #ifndef FEATURE_GROUPS_CUH_
 #define FEATURE_GROUPS_CUH_
@@ -29,22 +29,23 @@ struct FeatureGroup {
   /** The number of features in the group. */
   int num_features;
   /** The first bin in the group. */
-  int start_bin;
+  bst_bin_t start_bin;
   /** The number of bins in the group. */
-  int num_bins;
+  bst_bin_t num_bins;
 };
 
 /** \brief FeatureGroupsAccessor is a non-owning accessor for FeatureGroups. */
 struct FeatureGroupsAccessor {
   FeatureGroupsAccessor(common::Span<const int> feature_segments_,
-                       common::Span<const int> bin_segments_, int max_group_bins_) :
+                        common::Span<const int> bin_segments_, int max_group_bins_)
-    feature_segments(feature_segments_), bin_segments(bin_segments_),
+      : feature_segments(feature_segments_),
-    max_group_bins(max_group_bins_) {}
+        bin_segments(bin_segments_),
-  
+        max_group_bins(max_group_bins_) {}
+
   common::Span<const int> feature_segments;
   common::Span<const int> bin_segments;
   int max_group_bins;
-  
+
   /** \brief Gets the number of feature groups. */
   __host__ __device__ int NumGroups() const {
     return feature_segments.size() - 1;
@@ -84,7 +85,7 @@ struct FeatureGroups {
   /** Maximum number of bins in a group. Useful to compute the amount of dynamic
       shared memory when launching a kernel. */
   int max_group_bins;
-  
+
   /** Creates feature groups by splitting features into groups.
       \param cuts Histogram cuts that given the number of bins per feature.
       \param is_dense Whether the data matrix is dense.
@@ -110,7 +111,7 @@ struct FeatureGroups {
 
 private:
   void InitSingle(const common::HistogramCuts& cuts);
-}; 
+};
 
 }  // namespace tree
 }  // namespace xgboost

src/tree/gpu_hist/gradient_based_sampler.cu

@@ -167,7 +167,7 @@ GradientBasedSample ExternalMemoryNoSampling::Sample(Context const* ctx,
     for (auto& batch : dmat->GetBatches<EllpackPage>(ctx, batch_param_)) {
       auto page = batch.Impl();
       if (!page_) {
-        page_ = std::make_unique<EllpackPageImpl>(ctx->Device(), page->Cuts(), page->is_dense,
+        page_ = std::make_unique<EllpackPageImpl>(ctx->Device(), page->CutsShared(), page->is_dense,
                                                   page->row_stride, dmat->Info().num_row_);
       }
       size_t num_elements = page_->Copy(ctx->Device(), page, offset);
@@ -228,7 +228,7 @@ GradientBasedSample ExternalMemoryUniformSampling::Sample(Context const* ctx,
   auto first_page = (*batch_iterator.begin()).Impl();
   // Create a new ELLPACK page with empty rows.
   page_.reset();  // Release the device memory first before reallocating
-  page_.reset(new EllpackPageImpl(ctx->Device(), first_page->Cuts(), first_page->is_dense,
+  page_.reset(new EllpackPageImpl(ctx->Device(), first_page->CutsShared(), first_page->is_dense,
                                   first_page->row_stride, sample_rows));
 
   // Compact the ELLPACK pages into the single sample page.
@@ -306,7 +306,7 @@ GradientBasedSample ExternalMemoryGradientBasedSampling::Sample(Context const* c
   auto first_page = (*batch_iterator.begin()).Impl();
   // Create a new ELLPACK page with empty rows.
   page_.reset();  // Release the device memory first before reallocating
-  page_.reset(new EllpackPageImpl(ctx->Device(), first_page->Cuts(), first_page->is_dense,
+  page_.reset(new EllpackPageImpl(ctx->Device(), first_page->CutsShared(), first_page->is_dense,
                                   first_page->row_stride, sample_rows));
 
   // Compact the ELLPACK pages into the single sample page.

tests/cpp/common/test_hist_util.cu

@@ -56,8 +56,7 @@ TEST(HistUtil, DeviceSketch) {
 
 TEST(HistUtil, SketchBatchNumElements) {
 #if defined(XGBOOST_USE_RMM) && XGBOOST_USE_RMM == 1
-  LOG(WARNING) << "Test not runnable with RMM enabled.";
+  GTEST_SKIP_("Test not runnable with RMM enabled.");
-  return;
 #endif  // defined(XGBOOST_USE_RMM) && XGBOOST_USE_RMM == 1
   size_t constexpr kCols = 10000;
   int device;

tests/cpp/data/test_ellpack_page.cu

@@ -152,7 +152,7 @@ TEST(EllpackPage, Copy) {
   auto page = (*dmat->GetBatches<EllpackPage>(&ctx, param).begin()).Impl();
 
   // Create an empty result page.
-  EllpackPageImpl result(FstCU(), page->Cuts(), page->is_dense, page->row_stride, kRows);
+  EllpackPageImpl result(FstCU(), page->CutsShared(), page->is_dense, page->row_stride, kRows);
 
   // Copy batch pages into the result page.
   size_t offset = 0;
@@ -200,7 +200,8 @@ TEST(EllpackPage, Compact) {
   auto page = (*dmat->GetBatches<EllpackPage>(&ctx, param).begin()).Impl();
 
   // Create an empty result page.
-  EllpackPageImpl result(FstCU(), page->Cuts(), page->is_dense, page->row_stride, kCompactedRows);
+  EllpackPageImpl result(FstCU(), page->CutsShared(), page->is_dense, page->row_stride,
+                         kCompactedRows);
 
   // Compact batch pages into the result page.
   std::vector<size_t> row_indexes_h {

tests/cpp/data/test_ellpack_page_raw_format.cu

@@ -1,14 +1,14 @@
 /**
- * Copyright 2021-2023, XGBoost contributors
+ * Copyright 2021-2024, XGBoost contributors
  */
 #include <gtest/gtest.h>
 #include <xgboost/data.h>
 
 #include "../../../src/common/io.h"  // for PrivateMmapConstStream, AlignedResourceReadStream...
 #include "../../../src/data/ellpack_page.cuh"
-#include "../../../src/data/sparse_page_source.h"
+#include "../../../src/data/ellpack_page_raw_format.h"  // for EllpackPageRawFormat
-#include "../../../src/tree/param.h"  // TrainParam
+#include "../../../src/tree/param.h"                    // TrainParam
-#include "../filesystem.h"            // dmlc::TemporaryDirectory
+#include "../filesystem.h"                              // dmlc::TemporaryDirectory
 #include "../helpers.h"
 
 namespace xgboost::data {
@@ -16,12 +16,18 @@ TEST(EllpackPageRawFormat, IO) {
   Context ctx{MakeCUDACtx(0)};
   auto param = BatchParam{256, tree::TrainParam::DftSparseThreshold()};
 
-  std::unique_ptr<SparsePageFormat<EllpackPage>> format{CreatePageFormat<EllpackPage>("raw")};
-
   auto m = RandomDataGenerator{100, 14, 0.5}.GenerateDMatrix();
   dmlc::TemporaryDirectory tmpdir;
   std::string path = tmpdir.path + "/ellpack.page";
 
+  std::shared_ptr<common::HistogramCuts const> cuts;
+  for (auto const& page : m->GetBatches<EllpackPage>(&ctx, param)) {
+    cuts = page.Impl()->CutsShared();
+  }
+
+  cuts->SetDevice(ctx.Device());
+  auto format = std::make_unique<EllpackPageRawFormat>(cuts);
+
   std::size_t n_bytes{0};
   {
     auto fo = std::make_unique<common::AlignedFileWriteStream>(StringView{path}, "wb");
@@ -33,7 +39,7 @@ TEST(EllpackPageRawFormat, IO) {
   EllpackPage page;
   std::unique_ptr<common::AlignedResourceReadStream> fi{
       std::make_unique<common::PrivateMmapConstStream>(path.c_str(), 0, n_bytes)};
-  format->Read(&page, fi.get());
+  ASSERT_TRUE(format->Read(&page, fi.get()));
 
   for (auto const &ellpack : m->GetBatches<EllpackPage>(&ctx, param)) {
     auto loaded = page.Impl();

tests/cpp/data/test_gradient_index_page_raw_format.cc

@@ -7,23 +7,28 @@
 #include <cstddef>  // for size_t
 #include <memory>   // for unique_ptr
 
-#include "../../../src/common/column_matrix.h"
+#include "../../../src/common/column_matrix.h"  // for common::ColumnMatrix
-#include "../../../src/common/io.h"                // for MmapResource, AlignedResourceReadStream...
+#include "../../../src/common/io.h"             // for MmapResource, AlignedResourceReadStream...
-#include "../../../src/data/gradient_index.h"      // for GHistIndexMatrix
+#include "../../../src/data/gradient_index.h"   // for GHistIndexMatrix
-#include "../../../src/data/sparse_page_writer.h"  // for CreatePageFormat
+#include "../../../src/data/gradient_index_format.h"  // for GHistIndexRawFormat
-#include "../helpers.h"                            // for RandomDataGenerator
+#include "../helpers.h"                               // for RandomDataGenerator
 
 namespace xgboost::data {
 TEST(GHistIndexPageRawFormat, IO) {
   Context ctx;
 
-  std::unique_ptr<SparsePageFormat<GHistIndexMatrix>> format{
-      CreatePageFormat<GHistIndexMatrix>("raw")};
   auto m = RandomDataGenerator{100, 14, 0.5}.GenerateDMatrix();
   dmlc::TemporaryDirectory tmpdir;
   std::string path = tmpdir.path + "/ghistindex.page";
   auto batch = BatchParam{256, 0.5};
 
+  common::HistogramCuts cuts;
+  for (auto const &index : m->GetBatches<GHistIndexMatrix>(&ctx, batch)) {
+    cuts = index.Cuts();
+    break;
+  }
+  auto format = std::make_unique<GHistIndexRawFormat>(std::move(cuts));
+
   std::size_t bytes{0};
   {
     auto fo = std::make_unique<common::AlignedFileWriteStream>(StringView{path}, "wb");
@@ -36,7 +41,7 @@ TEST(GHistIndexPageRawFormat, IO) {
 
   std::unique_ptr<common::AlignedResourceReadStream> fi{
       std::make_unique<common::PrivateMmapConstStream>(path, 0, bytes)};
-  format->Read(&page, fi.get());
+  ASSERT_TRUE(format->Read(&page, fi.get()));
 
   for (auto const &gidx : m->GetBatches<GHistIndexMatrix>(&ctx, batch)) {
     auto const &loaded = gidx;

tests/cpp/data/test_iterative_dmatrix.cu

@@ -20,9 +20,8 @@ void TestEquivalent(float sparsity) {
                      std::numeric_limits<float>::quiet_NaN(), 0, 256);
   std::size_t offset = 0;
   auto first = (*m.GetEllpackBatches(&ctx, {}).begin()).Impl();
-  std::unique_ptr<EllpackPageImpl> page_concatenated {
+  std::unique_ptr<EllpackPageImpl> page_concatenated{new EllpackPageImpl(
-    new EllpackPageImpl(ctx.Device(), first->Cuts(), first->is_dense,
+      ctx.Device(), first->CutsShared(), first->is_dense, first->row_stride, 1000 * 100)};
-                        first->row_stride, 1000 * 100)};
   for (auto& batch : m.GetBatches<EllpackPage>(&ctx, {})) {
     auto page = batch.Impl();
     size_t num_elements = page_concatenated->Copy(ctx.Device(), page, offset);

tests/cpp/data/test_sparse_page_dmatrix.cc

@@ -171,6 +171,12 @@ TEST(SparsePageDMatrix, GHistIndexSkipSparsePage) {
     // Restore the batch parameter by passing it in again through check_ghist
     check_ghist();
   }
+  // half the pages
+  auto it = Xy->GetBatches<SparsePage>(&ctx).begin();
+  for (std::int32_t i = 0; i < 3; ++i) {
+    ++it;
+  }
+  check_ghist();
 }
 
 TEST(SparsePageDMatrix, MetaInfo) {

tests/cpp/data/test_sparse_page_dmatrix.cu

@@ -164,9 +164,9 @@ TEST(SparsePageDMatrix, EllpackPageContent) {
   size_t offset = 0;
   for (auto& batch : dmat_ext->GetBatches<EllpackPage>(&ctx, param)) {
     if (!impl_ext) {
-      impl_ext = std::make_unique<EllpackPageImpl>(batch.Impl()->gidx_buffer.Device(),
+      impl_ext = std::make_unique<EllpackPageImpl>(
-                                                   batch.Impl()->Cuts(), batch.Impl()->is_dense,
+          batch.Impl()->gidx_buffer.Device(), batch.Impl()->CutsShared(), batch.Impl()->is_dense,
-                                                   batch.Impl()->row_stride, kRows);
+          batch.Impl()->row_stride, kRows);
     }
     auto n_elems = impl_ext->Copy(ctx.Device(), batch.Impl(), offset);
     offset += n_elems;

tests/cpp/histogram_helpers.h

@@ -13,31 +13,25 @@
 
 namespace xgboost {
 #if defined(__CUDACC__)
-namespace {
+namespace detail {
 class HistogramCutsWrapper : public common::HistogramCuts {
  public:
   using SuperT = common::HistogramCuts;
-  void SetValues(std::vector<float> cuts) {
+  void SetValues(std::vector<float> cuts) { SuperT::cut_values_.HostVector() = std::move(cuts); }
-    SuperT::cut_values_.HostVector() = std::move(cuts);
+  void SetPtrs(std::vector<uint32_t> ptrs) { SuperT::cut_ptrs_.HostVector() = std::move(ptrs); }
-  }
+  void SetMins(std::vector<float> mins) { SuperT::min_vals_.HostVector() = std::move(mins); }
-  void SetPtrs(std::vector<uint32_t> ptrs) {
-    SuperT::cut_ptrs_.HostVector() = std::move(ptrs);
-  }
-  void SetMins(std::vector<float> mins) {
-    SuperT::min_vals_.HostVector() = std::move(mins);
-  }
 };
-}  //  anonymous namespace
+}  // namespace detail
 
 inline std::unique_ptr<EllpackPageImpl> BuildEllpackPage(int n_rows, int n_cols,
                                                          bst_float sparsity = 0) {
   auto dmat = RandomDataGenerator(n_rows, n_cols, sparsity).Seed(3).GenerateDMatrix();
   const SparsePage& batch = *dmat->GetBatches<xgboost::SparsePage>().begin();
 
-  HistogramCutsWrapper cmat;
+  auto cmat = std::make_shared<detail::HistogramCutsWrapper>();
-  cmat.SetPtrs({0, 3, 6, 9, 12, 15, 18, 21, 24});
+  cmat->SetPtrs({0, 3, 6, 9, 12, 15, 18, 21, 24});
   // 24 cut fields, 3 cut fields for each feature (column).
-  cmat.SetValues({0.30f, 0.67f, 1.64f,
+  cmat->SetValues({0.30f, 0.67f, 1.64f,
           0.32f, 0.77f, 1.95f,
           0.29f, 0.70f, 1.80f,
           0.32f, 0.75f, 1.85f,
@@ -45,7 +39,7 @@ inline std::unique_ptr<EllpackPageImpl> BuildEllpackPage(int n_rows, int n_cols,
           0.25f, 0.74f, 2.00f,
           0.26f, 0.74f, 1.98f,
           0.26f, 0.71f, 1.83f});
-  cmat.SetMins({0.1f, 0.2f, 0.3f, 0.1f, 0.2f, 0.3f, 0.2f, 0.2f});
+  cmat->SetMins({0.1f, 0.2f, 0.3f, 0.1f, 0.2f, 0.3f, 0.2f, 0.2f});
 
   bst_idx_t row_stride = 0;
   const auto &offset_vec = batch.offset.ConstHostVector();

tests/cpp/tree/test_gpu_hist.cu

@@ -150,13 +150,13 @@ TEST(GpuHist, BuildHistSharedMem) {
   TestBuildHist<GradientPairPrecise>(true);
 }
 
-HistogramCutsWrapper GetHostCutMatrix () {
+std::shared_ptr<detail::HistogramCutsWrapper> GetHostCutMatrix () {
-  HistogramCutsWrapper cmat;
+  auto cmat = std::make_shared<detail::HistogramCutsWrapper>();
-  cmat.SetPtrs({0, 3, 6, 9, 12, 15, 18, 21, 24});
+  cmat->SetPtrs({0, 3, 6, 9, 12, 15, 18, 21, 24});
-  cmat.SetMins({0.1f, 0.2f, 0.3f, 0.1f, 0.2f, 0.3f, 0.2f, 0.2f});
+  cmat->SetMins({0.1f, 0.2f, 0.3f, 0.1f, 0.2f, 0.3f, 0.2f, 0.2f});
   // 24 cut fields, 3 cut fields for each feature (column).
   // Each row of the cut represents the cuts for a data column.
-  cmat.SetValues({0.30f, 0.67f, 1.64f,
+  cmat->SetValues({0.30f, 0.67f, 1.64f,
               0.32f, 0.77f, 1.95f,
               0.29f, 0.70f, 1.80f,
               0.32f, 0.75f, 1.85f,