Hey, On Thu, Apr 04, 2013 at 01:37:50PM +0200, Michal Hocko wrote: > On Wed 03-04-13 17:13:08, Li Zefan wrote: > > Suppose we rmdir a cgroup and there're still css refs, this cgroup won't > > be freed. Then we rmdir the parent cgroup, and the parent is freed due > > to css ref draining to 0. Now it would be a disaster if the child cgroup > > tries to access its parent. > > Hmm, I am not sure what is the correct layer for this to handle - cgroup > core or memcg. But we have enforced that in mem_cgroup_css_online where > we take an additional reference to the memcg. > > Handling it in the memcg code would have an advantage of limiting an > additional reference only to use_hierarchy cases which is sufficient > as we never touch the parent otherwise (parent_mem_cgroup). But what harm does an additional reference do? And given that there are cgroup core interfaces which access ->parent, I think it'd be a good idea that parent always exists while there are children. Thanks. -- tejun -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>