[Panda] Before merge.
Merge branch 'master' of github.com:stpddream/OSHomework

Conflicts:
	hw4/mem_taichi/mem_util.h
[Panda] Before merge
Merge branch 'master' of github.com:stpddream/OSHomework

Conflicts:
	hw4/mem_taichi/mem.c
	hw4/mem_taichi/mem.h