在 2019/11/13 下午9:45, Matthew Wilcox 写道: >>> Why not simply: >>> >>> rcu_read_lock(); >>> lruvec = mem_cgroup_page_lruvec(page, pgdat); >>> rcu_read_unlock(); >>> >>> if (locked_lruvec == lruvec) >> The rcu_read_unlock here is for guarding the locked_lruvec/lruvec comparsion. >> Otherwise memcg/lruvec maybe changed, like, from memcg migration etc. I guess. > How does holding the RCU lock guard the comparison? You're comparing two > pointers for equality. Nothing any other CPU can do at this point will > change the results of that comparison. > Hi Matthew, Thanks for reply! The reason of guarding lruvec compasion here is a bit undistinct, in fact, it guards the page's memcg from free/migrate etc, since the lruvec is kind of binding to each of memcg. The detailed explanation could be found in lock_page_memcg(). Thanks Alex
