-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hello,

In the l4vfs source code I am sure that the malloc function could be used in the L4 programming. But I also find two functions named l4dm_mem_allocate and l4slab_alloc. It seems that both of them could also allocate memory as malloc does. What is the difference between the 3 functions? Which one is fastest? Please help me.

malloc() is provided by a standard C library. It typically mmap()s some anonymous memory and then performs memory allocation within this area. If the mmapped area is full, another piece of memory is retrieved. So, what libC needs to implement malloc() is a means to retrieve some memory from the underlying system. Our underlying L4 system's memory management is based on dataspaces provided by dataspace managers [1]. This is where l4dm_mem_allocate() comes in. It is used to allocate a dataspace from a dataspace manager (DSM). The DSM backs its dataspaces, e.g., dm_phys uses physical memory for that. The dataspace you get from your DSM is then attached to your local address space using l4rm_attach() - l4dm_mem_allocate() does this internally for you. Regarding speed: If you only do one allocation in your application, then both variants will be nearly the same speed, because malloc() will need to get backing storage using l4dm_mem_allocate(), or something similiar, first. This incorporates IPC to the dataspace manager and may include some page fault IPC(s) to your pager if you use the L4RM_MAP flag to map the new dataspace immediately. If you perform multiple allocations, malloc() will probably be faster in most cases, because it only performs bookkeeping inside your task, invoking no task switches, system calls etc. l4slab_alloc() comes from the L4 Slab implementation - this is an implementation of slab caches, which are described in [2]. Slabs are a fast way to allocate memory if you are dynamically allocating and freeing many same-sized small objects (e.g., objects of the same type). The slab implementation also uses dataspaces as underlying storage. Regards Bjoern [1] L4Env dataspaces documentation http://os.inf.tu-dresden.de/l4env/doc/html/dm_phys/index.html [2] J. Bonwick: "The slab allocator: an object-caching kernel memory allocator" http://www.usenix.org/publications/library/proceedings/bos94/full_papers/bon... -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFG5/XqP5ijxgQLUNkRAgztAJ9CJUS3YaixOhUl/N97UtlyWYU/pwCfZzJa Njw+GcN+EpDuZrccR7Wa4U4= =7cfq -----END PGP SIGNATURE-----