Dynamic memory allocation services

The implementation of the memory allocator follows the algorithm described in a USENIX 1988 paper called "Design of a General Purpose Memory Allocator for the 4.3BSD Unix Kernel" by Marshall K. More...

Collaboration diagram for Dynamic memory allocation services:

Functions
int	xnheap_init (struct xnheap *heap, void *membase, u32 size)
	Initialize a memory heap. More...
void	xnheap_set_name (struct xnheap *heap, const char *name,...)
	Set the heap's name string. More...
void	xnheap_destroy (struct xnheap *heap)
	Destroys a memory heap. More...
void *	xnheap_alloc (struct xnheap *heap, u32 size)
	Allocate a memory block from a memory heap. More...
void	xnheap_free (struct xnheap *heap, void *block)
	Release a block to a memory heap. More...

Detailed Description

The implementation of the memory allocator follows the algorithm described in a USENIX 1988 paper called "Design of a General Purpose Memory Allocator for the 4.3BSD Unix Kernel" by Marshall K.

McKusick and Michael J. Karels. You can find it at various locations on the net, including http://docs.FreeBSD.org/44doc/papers/kernmalloc.pdf.

Implementation constraints

• Minimum page size is 2 ** XNHEAP_MINLOG2 (must be large enough to hold a pointer).
• Maximum page size is 2 ** XNHEAP_MAXLOG2.
• Requested block size is rounded up to XNHEAP_MINLOG2.
• Requested block size larger than 2 times the XNHEAP_PAGESZ is rounded up to the next page boundary and obtained from the free page list. So we need a bucket for each power of two between XNHEAP_MINLOG2 and XNHEAP_MAXLOG2 inclusive, plus one to honor requests ranging from the maximum page size to twice this size.

Function Documentation

xnheap_alloc()

void * xnheap_alloc	(	struct xnheap *	heap,
		u32	size
	)

Allocate a memory block from a memory heap.

Allocates a contiguous region of memory from an active memory heap. Such allocation is guaranteed to be time-bounded.

Parameters

heap	The descriptor address of the heap to get memory from.
size	The size in bytes of the requested block. Sizes lower or equal to the page size are rounded either to the minimum allocation size if lower than this value, or to the minimum alignment size if greater or equal to this value. In the current implementation, with MINALLOC = 8 and MINALIGN = 16, a 7 bytes request will be rounded to 8 bytes, and a 17 bytes request will be rounded to 32.

Returns

The address of the allocated region upon success, or NULL if no memory is available from the specified heap.

Tags

unrestricted

xnheap_destroy()

void xnheap_destroy

(

struct xnheap *

heap

)

Destroys a memory heap.

Destroys a memory heap.

Parameters

heap	The heap descriptor.

Tags

secondary-only

xnheap_free()

void xnheap_free	(	struct xnheap *	heap,
		void *	block
	)

Release a block to a memory heap.

Releases a memory block to a heap.

Parameters

heap	The heap descriptor.
block	The block to be returned to the heap.

Tags

unrestricted

xnheap_init()

int xnheap_init	(	struct xnheap *	heap,
		void *	membase,
		u32	size
	)

Initialize a memory heap.

Initializes a memory heap suitable for time-bounded allocation requests of dynamic memory.

Parameters

heap	The address of a heap descriptor to initialize.
membase	The address of the storage area.
size	The size in bytes of the storage area. size must be a multiple of PAGE_SIZE and smaller than 2 Gb in the current implementation.

Returns

0 is returned upon success, or:

• -EINVAL is returned if size is either:
  • not aligned on PAGE_SIZE
  • smaller than 2 * PAGE_SIZE
  • greater than 2 Gb (XNHEAP_MAXHEAPSZ)
• -ENOMEM is returned upon failure of allocating the meta-data area used internally to maintain the heap.

Tags

secondary-only

xnheap_set_name()

void xnheap_set_name	(	struct xnheap *	heap,
		const char *	name,
			...
	)

Set the heap's name string.

Set the heap name that will be used in statistic outputs.

Parameters

heap	The address of a heap descriptor.
name	Name displayed in statistic outputs. This parameter can be a printk()-like format argument list.

Tags

task-unrestricted