On Fri 28-09-12 15:34:19, Glauber Costa wrote: > On 09/27/2012 05:44 PM, Michal Hocko wrote: > >> > the reference count aquired by mem_cgroup_get will still prevent the > >> > memcg from going away, no? > > Yes but you are outside of the rcu now and we usually do css_get before > > we rcu_unlock. mem_cgroup_get just makes sure the group doesn't get > > deallocated but it could be gone before you call it. Or I am just > > confused - these 2 levels of ref counting is really not nice. > > > > Anyway, I have just noticed that __mem_cgroup_try_charge does > > VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should > > keep css ref count up as well. > > > > IIRC, css_get will prevent the cgroup directory from being removed. > Because some allocations are expected to outlive the cgroup, we > specifically don't want that. Yes, but how do you guarantee that the above VM_BUG_ON doesn't trigger? Task could have been moved to another group between mem_cgroup_from_task and mem_cgroup_get, no? -- Michal Hocko SUSE Labs -- 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>