From 47f64cf0b595ab3b462ae96abcf90f9fa8ed2ffd Mon Sep 17 00:00:00 2001 From: Lysandros Nikolaou Date: Wed, 25 Feb 2026 17:15:33 +0100 Subject: [PATCH] gh-142518: Improve mimalloc allocator docs --- Doc/c-api/memory.rst | 58 ++++++++++++++++++++++++++++++----------- Doc/using/cmdline.rst | 20 +++++++++++--- Doc/using/configure.rst | 3 +++ 3 files changed, 63 insertions(+), 18 deletions(-) diff --git a/Doc/c-api/memory.rst b/Doc/c-api/memory.rst index 563c5d96b05362..52c8fc26eb673f 100644 --- a/Doc/c-api/memory.rst +++ b/Doc/c-api/memory.rst @@ -205,7 +205,9 @@ behavior when requesting zero bytes, are available for allocating and releasing memory from the Python heap. The :ref:`default memory allocator ` uses the -:ref:`pymalloc memory allocator `. +:ref:`pymalloc memory allocator `. In the +:term:`free-threaded ` build, the default is the +:ref:`mimalloc memory allocator ` instead. .. warning:: @@ -215,6 +217,11 @@ The :ref:`default memory allocator ` uses the The default allocator is now pymalloc instead of system :c:func:`malloc`. +.. versionchanged:: 3.13 + + In the :term:`free-threaded ` build, the default allocator + is now :ref:`mimalloc `. + .. c:function:: void* PyMem_Malloc(size_t n) Allocates *n* bytes and returns a pointer of type :c:expr:`void*` to the @@ -340,7 +347,9 @@ memory from the Python heap. the :ref:`Customize Memory Allocators ` section. The :ref:`default object allocator ` uses the -:ref:`pymalloc memory allocator `. +:ref:`pymalloc memory allocator `. In the +:term:`free-threaded ` build, the default is the +:ref:`mimalloc memory allocator ` instead. .. warning:: @@ -420,14 +429,16 @@ Default Memory Allocators Default memory allocators: -=============================== ==================== ================== ===================== ==================== -Configuration Name PyMem_RawMalloc PyMem_Malloc PyObject_Malloc -=============================== ==================== ================== ===================== ==================== -Release build ``"pymalloc"`` ``malloc`` ``pymalloc`` ``pymalloc`` -Debug build ``"pymalloc_debug"`` ``malloc`` + debug ``pymalloc`` + debug ``pymalloc`` + debug -Release build, without pymalloc ``"malloc"`` ``malloc`` ``malloc`` ``malloc`` -Debug build, without pymalloc ``"malloc_debug"`` ``malloc`` + debug ``malloc`` + debug ``malloc`` + debug -=============================== ==================== ================== ===================== ==================== +=================================== ======================= ================== ===================== ==================== +Configuration Name PyMem_RawMalloc PyMem_Malloc PyObject_Malloc +=================================== ======================= ================== ===================== ==================== +Release build ``"pymalloc"`` ``malloc`` ``pymalloc`` ``pymalloc`` +Debug build ``"pymalloc_debug"`` ``malloc`` + debug ``pymalloc`` + debug ``pymalloc`` + debug +Release build, without pymalloc ``"malloc"`` ``malloc`` ``malloc`` ``malloc`` +Debug build, without pymalloc ``"malloc_debug"`` ``malloc`` + debug ``malloc`` + debug ``malloc`` + debug +Free-threaded build ``"mimalloc"`` ``malloc`` ``mimalloc`` ``mimalloc`` +Free-threaded debug build ``"mimalloc_debug"`` ``malloc`` + debug ``mimalloc`` + debug ``mimalloc`` + debug +=================================== ======================= ================== ===================== ==================== Legend: @@ -435,8 +446,7 @@ Legend: * ``malloc``: system allocators from the standard C library, C functions: :c:func:`malloc`, :c:func:`calloc`, :c:func:`realloc` and :c:func:`free`. * ``pymalloc``: :ref:`pymalloc memory allocator `. -* ``mimalloc``: :ref:`mimalloc memory allocator `. The pymalloc - allocator will be used if mimalloc support isn't available. +* ``mimalloc``: :ref:`mimalloc memory allocator `. * "+ debug": with :ref:`debug hooks on the Python memory allocators `. * "Debug build": :ref:`Python build in debug mode `. @@ -733,9 +743,27 @@ The mimalloc allocator .. versionadded:: 3.13 -Python supports the mimalloc allocator when the underlying platform support is available. -mimalloc "is a general purpose allocator with excellent performance characteristics. -Initially developed by Daan Leijen for the runtime systems of the Koka and Lean languages." +Python supports the `mimalloc `__ +allocator when the underlying platform support is available. +mimalloc is a general purpose allocator with excellent performance +characteristics, initially developed by Daan Leijen for the runtime systems +of the Koka and Lean languages. + +Unlike :ref:`pymalloc `, which is optimized for small objects (512 +bytes or fewer), mimalloc handles allocations of any size. + +In the :term:`free-threaded ` build, mimalloc is the default +and **required** allocator for the :c:macro:`PYMEM_DOMAIN_MEM` and +:c:macro:`PYMEM_DOMAIN_OBJ` domains. It cannot be disabled in free-threaded +builds. The free-threaded build uses per-thread mimalloc heaps, which allows +allocation and deallocation to proceed without locking in most cases. + +In the default (non-free-threaded) build, mimalloc is available but not the +default allocator. It can be selected at runtime using +:envvar:`PYTHONMALLOC`\ ``=mimalloc`` (or ``mimalloc_debug`` to include +:ref:`debug hooks `). It can be disabled at build time +using the :option:`--without-mimalloc` configure option, but this option +cannot be combined with :option:`--disable-gil`. tracemalloc C API ================= diff --git a/Doc/using/cmdline.rst b/Doc/using/cmdline.rst index 2e7ea7b4fc4cba..87d879d12e16d3 100644 --- a/Doc/using/cmdline.rst +++ b/Doc/using/cmdline.rst @@ -1074,21 +1074,35 @@ conflict. * ``pymalloc_debug``: same as ``pymalloc`` but also install debug hooks. * ``mimalloc_debug``: same as ``mimalloc`` but also install debug hooks. + .. note:: + + In the :term:`free-threaded ` build, the ``malloc``, + ``malloc_debug``, ``pymalloc``, and ``pymalloc_debug`` values are not + supported. Only ``default``, ``debug``, ``mimalloc``, and + ``mimalloc_debug`` are accepted. + .. versionadded:: 3.6 .. versionchanged:: 3.7 Added the ``"default"`` allocator. + .. versionchanged:: 3.13 + Added the ``"mimalloc"`` and ``"mimalloc_debug"`` allocators. + In the :term:`free-threaded ` build, the ``"malloc"``, + ``"malloc_debug"``, ``"pymalloc"``, and ``"pymalloc_debug"`` values are + not accepted. + .. envvar:: PYTHONMALLOCSTATS If set to a non-empty string, Python will print statistics of the - :ref:`pymalloc memory allocator ` every time a new pymalloc object - arena is created, and on shutdown. + :ref:`pymalloc memory allocator ` or the + :ref:`mimalloc memory allocator ` (whichever is in use) + every time a new object arena is created, and on shutdown. This variable is ignored if the :envvar:`PYTHONMALLOC` environment variable is used to force the :c:func:`malloc` allocator of the C library, or if - Python is configured without ``pymalloc`` support. + Python is configured without both ``pymalloc`` and ``mimalloc`` support. .. versionchanged:: 3.6 This variable can now also be used on Python compiled in release mode. diff --git a/Doc/using/configure.rst b/Doc/using/configure.rst index 813127663ed8fe..6bef290d181fc9 100644 --- a/Doc/using/configure.rst +++ b/Doc/using/configure.rst @@ -774,6 +774,9 @@ also be used to improve performance. Disable the fast :ref:`mimalloc ` allocator (enabled by default). + This option cannot be used together with :option:`--disable-gil` + because the :term:`free-threaded ` build requires mimalloc. + See also :envvar:`PYTHONMALLOC` environment variable. .. option:: --without-pymalloc