Fix dataset deserialize not owning the data

cpp/include/cuvs/neighbors/common.hpp

@@ -264,6 +264,77 @@ auto make_strided_dataset(const raft::resources& res, const SrcT& src, uint32_t
   return std::make_unique<out_owning_type>(std::move(out_array), out_layout);
 }
 
+/**
+ * @brief Contstruct a strided matrix from any mdarray.
+ *
+ * This function constructs an owning device matrix and copies the data.
+ * When the data is copied, padding elements are filled with zeroes.
+ *
+ * @tparam DataT
+ * @tparam IdxT
+ * @tparam LayoutPolicy
+ * @tparam ContainerPolicy
+ *
+ * @param[in] res raft resources handle
+ * @param[in] src the source mdarray or mdspan
+ * @param[in] required_stride the leading dimension (in elements)
+ * @return owning current-device-accessible strided matrix
+ */
+template <typename DataT, typename IdxT, typename LayoutPolicy, typename ContainerPolicy>
+auto make_strided_dataset(
+  const raft::resources& res,
+  raft::mdarray<DataT, raft::matrix_extent<IdxT>, LayoutPolicy, ContainerPolicy>&& src,
+  uint32_t required_stride) -> std::unique_ptr<strided_dataset<DataT, IdxT>>
+{
+  using value_type            = DataT;
+  using index_type            = IdxT;
+  using layout_type           = LayoutPolicy;
+  using container_policy_type = ContainerPolicy;
+  static_assert(std::is_same_v<layout_type, raft::layout_right> ||
+                  std::is_same_v<layout_type, raft::layout_right_padded<value_type>> ||
+                  std::is_same_v<layout_type, raft::layout_stride>,
+                "The input must be row-major");
+  RAFT_EXPECTS(src.extent(1) <= required_stride,
+               "The input row length must be not larger than the desired stride.");
+  const uint32_t src_stride = src.stride(0) > 0 ? src.stride(0) : src.extent(1);
+  const bool stride_matches = required_stride == src_stride;
+
+  auto out_layout =
+    raft::make_strided_layout(src.extents(), std::array<index_type, 2>{required_stride, 1});
+
+  using out_mdarray_type          = raft::device_matrix<value_type, index_type>;
+  using out_layout_type           = typename out_mdarray_type::layout_type;
+  using out_container_policy_type = typename out_mdarray_type::container_policy_type;
+  using out_owning_type =
+    owning_dataset<value_type, index_type, out_layout_type, out_container_policy_type>;
+
+  if constexpr (std::is_same_v<layout_type, out_layout_type> &&
+                std::is_same_v<container_policy_type, out_container_policy_type>) {
+    if (stride_matches) {
+      // Everything matches, we can own the mdarray
+      return std::make_unique<out_owning_type>(std::move(src), out_layout);
+    }
+  }
+  // Something is wrong: have to make a copy and produce an owning dataset
+  auto out_array =
+    raft::make_device_matrix<value_type, index_type>(res, src.extent(0), required_stride);
+
+  RAFT_CUDA_TRY(cudaMemsetAsync(out_array.data_handle(),
+                                0,
+                                out_array.size() * sizeof(value_type),
+                                raft::resource::get_cuda_stream(res)));
+  RAFT_CUDA_TRY(cudaMemcpy2DAsync(out_array.data_handle(),
+                                  sizeof(value_type) * required_stride,
+                                  src.data_handle(),
+                                  sizeof(value_type) * src_stride,
+                                  sizeof(value_type) * src.extent(1),
+                                  src.extent(0),
+                                  cudaMemcpyDefault,
+                                  raft::resource::get_cuda_stream(res)));
+
+  return std::make_unique<out_owning_type>(std::move(out_array), out_layout);
+}
+
 /**
  * @brief Contstruct a strided matrix from any mdarray or mdspan.
  *
@@ -278,14 +349,15 @@ auto make_strided_dataset(const raft::resources& res, const SrcT& src, uint32_t
  * @return maybe owning current-device-accessible strided matrix
  */
 template <typename SrcT>
-auto make_aligned_dataset(const raft::resources& res, const SrcT& src, uint32_t align_bytes = 16)
+auto make_aligned_dataset(const raft::resources& res, SrcT src, uint32_t align_bytes = 16)
   -> std::unique_ptr<strided_dataset<typename SrcT::value_type, typename SrcT::index_type>>
 {
-  using value_type       = typename SrcT::value_type;
+  using source_type      = std::remove_cv_t<std::remove_reference_t<SrcT>>;
+  using value_type       = typename source_type::value_type;
   constexpr size_t kSize = sizeof(value_type);
   uint32_t required_stride =
     raft::round_up_safe<size_t>(src.extent(1) * kSize, std::lcm(align_bytes, kSize)) / kSize;
-  return make_strided_dataset(res, src, required_stride);
+  return make_strided_dataset(res, std::forward<SrcT>(src), required_stride);
 }
 /**
  * @brief VPQ compressed dataset.

cpp/src/neighbors/detail/dataset_serialize.hpp

@@ -140,7 +140,7 @@ auto deserialize_strided(raft::resources const& res, std::istream& is)
   auto stride     = raft::deserialize_scalar<uint32_t>(res, is);
   auto host_array = raft::make_host_matrix<DataT, IdxT>(n_rows, dim);
   raft::deserialize_mdspan(res, is, host_array.view());
-  return make_strided_dataset(res, host_array, stride);
+  return make_strided_dataset(res, std::move(host_array), stride);
 }
 
 template <typename MathT, typename IdxT>