vend               12 kalloc.c       void freerange(void *vstart, void *vend);
vend               32 kalloc.c       kinit1(void *vstart, void *vend)
vend               36 kalloc.c         freerange(vstart, vend);
vend               40 kalloc.c       kinit2(void *vstart, void *vend)
vend               42 kalloc.c         freerange(vstart, vend);
vend               47 kalloc.c       freerange(void *vstart, void *vend)
vend               51 kalloc.c         for(; p + PGSIZE <= (char*)vend; p += PGSIZE)