vend               12 kalloc.c       void freerange(void *vstart, void *vend);
vend               31 kalloc.c       kinit1(void *vstart, void *vend)
vend               35 kalloc.c         freerange(vstart, vend);
vend               39 kalloc.c       kinit2(void *vstart, void *vend)
vend               41 kalloc.c         freerange(vstart, vend);
vend               46 kalloc.c       freerange(void *vstart, void *vend)
vend               50 kalloc.c         for(; p + PGSIZE <= (char*)vend; p += PGSIZE)