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heap: clean up some size related issues

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First, the maximum heap size must fit in 31 bits worth of chunks
because the internal 32-bit field holding the size is shared with
the `used` bit.

Then the mention of a 256-byte block in the doc is no longer
relevant. That pertained to the previous allocator implementation.

And ditto for the HEAP_MEM_POOL_MIN_SIZE kconfig option.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
This commit is contained in:
Nicolas Pitre 2021-01-13 17:19:10 -05:00 • committed by Anas Nashif
commit 7a22a4bdf6
3 changed files with 4 additions and 17 deletions
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8
doc/reference/kernel/memory/heap.rst
View file

@ -102,7 +102,7 @@ The :dfn:`system heap` is a predefined memory allocator that allows
threads to dynamically allocate memory from a common memory region in
a :c:func:`malloc`-like manner.
Only a single system heap is be defined. Unlike other heaps or memory
Only a single system heap is defined. Unlike other heaps or memory
pools, the system heap cannot be directly referenced using its
memory address.
@ -136,9 +136,6 @@ A chunk of heap memory is allocated by calling :c:func:`k_malloc`.
The following code allocates a 200 byte chunk of heap memory, then fills it
with zeros. A warning is issued if a suitable chunk is not obtained.
Note that the application will actually allocate a 256 byte memory block,
since that is the closest matching size supported by the heap memory pool.
.. code-block:: c
char *mem_ptr;
@ -157,8 +154,7 @@ Releasing Memory
A chunk of heap memory is released by calling :c:func:`k_free`.
The following code allocates a 75 byte chunk of memory, then releases it
once it is no longer needed. (A 256 byte memory block from the heap memory
pool is actually used to satisfy the request.)
once it is no longer needed.
.. code-block:: c

9
kernel/Kconfig
View file

@ -512,15 +512,6 @@ config HEAP_MEM_POOL_SIZE
the memory pool is only limited to available memory. A size of zero
means that no heap memory pool is defined.
config HEAP_MEM_POOL_MIN_SIZE
int "The smallest blocks in the heap memory pool (in bytes)"
depends on HEAP_MEM_POOL_SIZE != 0
default 64
help
This option specifies the size of the smallest block in the pool.
Option must be a power of 2 and lower than or equal to the size
of the entire pool.
endif # KERNEL_MEM_POOL
endmenu

4
lib/os/heap.c
View file

@ -351,8 +351,8 @@ void *sys_heap_realloc(struct sys_heap *heap, void *ptr, size_t bytes)
void sys_heap_init(struct sys_heap *heap, void *mem, size_t bytes)
{
/* Must fit in a 32 bit count of HUNK_UNIT */
__ASSERT(bytes / CHUNK_UNIT <= 0xffffffffU, "heap size is too big");
/* Must fit in a 31 bit count of HUNK_UNIT */
__ASSERT(bytes / CHUNK_UNIT <= 0x7fffffffU, "heap size is too big");
/* Reserve the final marker chunk's header */
__ASSERT(bytes > heap_footer_bytes(bytes), "heap size is too small");