:orphan:

.. title:: choice: Supported heap sizes

.. _choice_412:

.. describe:: choice: Supported heap sizes

*Supported heap sizes*

Type: ``bool``

Help
====

.. code-block:: none

    Heaps using reduced-size chunk headers can accommodate so called
    "small" heaps with a total size of 262136 bytes or less.

    Heaps using full-size chunk headers can have a total size up to
    16383 megabytes. The overhead is of course bigger.

    On 32-bit system the tradeoff is selectable between:

    - "small" heaps with low memory and runtime overhead;

    - "big" heaps with bigger memory overhead even for small heaps;

    - "auto" providing optimal memory overhead in all cases but with
      a higher runtime overhead and somewhat bigger code footprint.

    On 64-bit systems the "big" chunk header size conveniently provides
    the needed alignment on returned memory allocations. Small chunk
    headers would require alignment padding up to the big header size
    anyway so "big" heap is the only option in that case.

Direct dependencies
===================

!\ :kconfig:`64BIT <CONFIG_64BIT>`

*(Includes any dependencies from ifs and menus.)*

Defaults
========

- \ :kconfig:`SYS_HEAP_SMALL_ONLY <CONFIG_SYS_HEAP_SMALL_ONLY>` if \ :kconfig:`SRAM_SIZE <CONFIG_SRAM_SIZE>` <= 256
- \ :kconfig:`SYS_HEAP_AUTO <CONFIG_SYS_HEAP_AUTO>`

Choice options
==============

- \ :kconfig:`SYS_HEAP_SMALL_ONLY <CONFIG_SYS_HEAP_SMALL_ONLY>`
- \ :kconfig:`SYS_HEAP_BIG_ONLY <CONFIG_SYS_HEAP_BIG_ONLY>`
- \ :kconfig:`SYS_HEAP_AUTO <CONFIG_SYS_HEAP_AUTO>`

Kconfig definition
==================



At ``<Library>/os/Kconfig.heap:51``

Included via ``Kconfig:8`` → ``Kconfig.zephyr:43`` → ``<Library>/Kconfig:10`` → ``<Library>/os/Kconfig:88``

Menu path: (Top) → Additional libraries → OS Support Library → Heap and Memory Allocation

.. code-block:: kconfig

    choice
    	bool "Supported heap sizes"
    	default SYS_HEAP_SMALL_ONLY if SRAM_SIZE <= 256
    	default SYS_HEAP_AUTO
    	depends on !64BIT
    	help
    	  Heaps using reduced-size chunk headers can accommodate so called
    	  "small" heaps with a total size of 262136 bytes or less.
	  
    	  Heaps using full-size chunk headers can have a total size up to
    	  16383 megabytes. The overhead is of course bigger.
	  
    	  On 32-bit system the tradeoff is selectable between:
	  
    	  - "small" heaps with low memory and runtime overhead;
	  
    	  - "big" heaps with bigger memory overhead even for small heaps;
	  
    	  - "auto" providing optimal memory overhead in all cases but with
    	    a higher runtime overhead and somewhat bigger code footprint.
	  
    	  On 64-bit systems the "big" chunk header size conveniently provides
    	  the needed alignment on returned memory allocations. Small chunk
    	  headers would require alignment padding up to the big header size
    	  anyway so "big" heap is the only option in that case.

*(The 'depends on' condition includes propagated dependencies from ifs and menus.)*