rockbox/lib/tlsf/README

TLSF Memory Storage allocator implementation.
Version 2.4 Feb 2008

Authors: Miguel Masmano, Ismael Ripoll & Alfons Crespo.
Copyright UPVLC, OCERA Consortium.

TLSF is released in the GPL/LGPL licence. The exact terms of the licence
are described in the COPYING file.

This component provides basic memory allocation functions:
malloc and free, as defined in the standard "C" library.

This allocator was designed to provide real-time performance, that is:
1.- Bounded time malloc and free.
2.- Fast response time.
3.- Efficient memory management, that is low fragmentation.


The worst response time for both malloc and free is O(1).



How to use it:

This code  is prepared to  be used as  a stand-alone code that  can be
linked with a regular application or  it can be compiled to be a Linux
module  (which  required the  BigPhysicalArea  patch).  Initially  the
module was  designed to  work jointly with  RTLinux-GPL, but it  can be
used as a stand alone Linux module.

When compiled as a regular linux process the API is:

Initialisation and destruction functions
----------------------------------------

init_memory_pool may be called before any request or release call:

- size_t init_memory_pool(size_t, void *);
- void destroy_memory_pool(void *);

Request and release functions
-----------------------------

As can be seen, there are two functions for each traditional memory
allocation function (malloc, free, realloc, and calloc). One with the
prefix "tlsf_" and the other with the suffix "_ex". 

The versions with the prefix "tlsf_" provides the expected behaviour,
that is, allocating/releasing memory from the default memory pool. The
default memory pool is the last pool initialised by the
init_memory_pool function.

On the other hand, the functions with the prefix "_ex" enable the use of several memory pools.

- void *tlsf_malloc(size_t);
- void *malloc_ex(size_t, void *);

- void tlsf_free(void *ptr);
- void free_ex(void *, void *);

- void *tlsf_realloc(void *ptr, size_t size);
- void *realloc_ex(void *, size_t, void *);

- void *tlsf_calloc(size_t nelem, size_t elem_size);
- void *calloc_ex(size_t, size_t, void *);

EXAMPLE OF USE:

char memory_pool[1024*1024];

{
	...

	init_memory_pool(1024*1024, memory_pool);

	...
	
	ptr1=malloc_ex(100, memory_pool);
	ptr2=tlsf_malloc(100); // This function will use memory_pool
	
        ...

        tlsf_free(ptr2);
	free_ex(ptr1, memory_pool);
}

Growing the memory pool
-----------------------

Starting from the version 2.4, the function add_new_area adds an
memory area to an existing memory pool.

- size_t add_new_area(void *, size_t, void *);

This feature is pretty useful when an existing memory pool is running
low and we want to add more free memory to it.
EXAMPLE OF USE:

char memory_pool[1024*1024];
char memory_pool2[1024*1024];

{
	...

	init_memory_pool(1024*1024, memory_pool);

	...
	
	ptr[0]=malloc_ex(1024*256 memory_pool); 
	ptr[1]=malloc_ex(1024*512, memory_pool); 
	add_new_area(memory_pool2, 1024*1024, memory_pool);
	// Now we have an extra free memory area of 1Mb
	// The next malloc may not fail
	ptr[2]=malloc_ex(1024*512, memory_pool); 
	
        ...

}


SBRK and MMAP support
---------------------

The version 2.4 can use the functions SBRK and MMAP to _automatically_
growing the memory pool, before running out of memory.

So, when this feature is enabled, unless the operating system were out
of memory, a malloc operation would not fail due to an "out-of-memory"
error.

To enable this support, compile tlsf.c with the FLAGS -DUSE_MMAP=1 or
-DUSE_SBRK=1 depending on whether you want to use "mmap" or "sbrk" or both.

** By default (default Makefile) this feature is enabled.

EXAMPLE OF USE:

gcc -o tlsf.o -O2 -Wall -DUSE_MMAP=1 -DUSE_SBRK=1

---

If the sbrk/mmap support is enabled and we are _only_ going to use one
memory pool, it is not necessary to call init_memory_pool

EXAMPLE OF USE (with MMAP/SBRK support enabled):

{
	...
	
	ptr2=tlsf_malloc(100); // This function will use memory_pool
	
        ...

        tlsf_free(ptr2);
}




This work has been supported by the followin projects:
EUROPEAN: IST-2001-35102(OCERA) http://www.ocera.org.
SPANISH: TIN2005-08665-C3-03