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.. meta::
  :description: Overview of the libhipcxx memory resource extended API, providing a standard C++ interface for heterogeneous, stream-ordered memory allocation in HIP.
  :keywords: libhipcxx, ROCm, HIP, C++, memory resource, cuda::mr, async_resource, resource_ref, stream-ordered allocation


.. _libcudacxx-extended-api-memory-resources:

Memory Resources
================

This page covers the memory resource extended API, providing a standard C++ interface for heterogeneous, stream-ordered memory allocation in HIP.

.. toctree::
   :hidden:
   :maxdepth: 1

   memory_resource/properties
   Resources <memory_resource/resource>
   Resource wrapper <memory_resource/resource_ref>

..
   The ``<cuda/memory_resource>`` header provides a standard C++ interface for *heterogeneous*, *stream-ordered* memory
   allocation tailored to the needs of CUDA C++ developers. This design builds off of the success of the `RAPIDS Memory Manager (RMM) <https://github.com/rapidsai/rmm>`__
   project and evolves the design based on lessons learned.
The ``<cuda/memory_resource>`` header provides a standard C++ interface for *heterogeneous*, *stream-ordered* memory
allocation tailored to the needs of HIP C++ developers.

``<cuda/memory_resource>`` only defines the memory allocation interface; it does not provide allocator
implementations. For HIP developers, `hipMM <https://github.com/AMD-Ecosystem/hipMM>`__ provides implementations of
the ``cuda::mr`` interfaces optimized for AMD GPUs.

We are still experimenting with the design, so for now the contents of ``<cuda/memory_resource>`` are only available if
``LIBCUDACXX_ENABLE_EXPERIMENTAL_MEMORY_RESOURCE`` is defined.

At a high level, the header provides:

.. list-table::
   :widths: 30 50 20
   :header-rows: 1

   * - API
     - Description
     - Since

   * - :ref:`cuda::get_property <libcudacxx-extended-api-memory-resources-properties>`
     - Infrastructure to tag a user defined type with a given property
     - libhipcxx 2.7
   * - :ref:`cuda::mr::{async}_resource <libcudacxx-extended-api-memory-resources-resource>` and
       :ref:`cuda::mr::{async}_resource_with <libcudacxx-extended-api-memory-resources-resource>`
     - Concepts that provide proper constraints for arbitrary memory resources.
     - libhipcxx 2.7
   * - :ref:`cuda::mr::{async}_resource_ref <libcudacxx-extended-api-memory-resources-resource-ref>`
     - A non-owning type-erased memory resource wrapper that enables consumers to specify properties of resources that they expect.
     - libhipcxx 2.7

These features are an evolution of `std::pmr::memory_resource <https://en.cppreference.com/w/cpp/header/memory_resource>`__
that was introduced in C++17. While ``std::pmr::memory_resource`` provides a polymorphic memory resource that can be
adopted through inheritance, it is not properly suited for heterogeneous systems.

With the current design it ranges from cumbersome to impossible to verify whether a memory resource provides allocations
that are e.g. accessible on device, or whether it can utilize other allocation mechanisms.

To better support asynchronous HIP `stream-ordered allocations <https://rocm.docs.amd.com/projects/HIP/en/latest/how-to/hip_runtime_api/memory_management/stream_ordered_allocator.html>`__
libhipcxx provides :ref:`cuda::stream_ref <libcudacxx-extended-api-streams-stream-ref>` as a wrapper around
``hipStream_t``. The definition of ``cuda::stream_ref`` can be found in the ``<cuda/stream_ref>`` header.