MALLOC_FREE
if (page_dir[ptr2idx(pf->page)] != MALLOC_FREE)
if (page_dir[ptr2idx(pf->end)-1] != MALLOC_FREE)
if (p != NULL && page_dir[ptr2idx(p)] != MALLOC_FREE)
if (info == MALLOC_FREE) {
page_dir[idx] = MALLOC_FREE;
page_dir[idx + i] = MALLOC_FREE;