Malloc:
  I have refer to http://www.inf.udec.cl/~leo/Malloc_tutorial.pdf this suppot
when I do this project. We know that each process has its own virtual adress 
space dynamically translated into physical memory adress space by the MMU (and 
the kernel.) And for controling the distribution of memory, I need
implementation metadata in each memory allocated, and I chose algo first-fit, 
it's less difficult.
  I think a difficult point is function free, how recover all the memory and how
make it duplicate, these question make me confuse, mb I spent too much time in
compilation instead of comprehension, I did my best.