40. ページカラーリング実装
* o free
* => pageq.list is entry on global free page queue
* => listq.list is entry on per-CPU free page queue
* => uanon is unused (or (void *)0xdeadbeef for DEBUG)
* => uobject is unused (or (void *)0xdeadbeef for DEBUG)
* => PQ_FREE is set in pqflags
uvm.page_free
と
ucpu->page_free
の二つの空きページリストに登録
uvm_pagefree()