On Mon 16-12-13 17:41:38, Hugh Dickins wrote: > On Mon, 16 Dec 2013, Tejun Heo wrote: > > On Mon, Dec 16, 2013 at 06:19:37PM +0100, Michal Hocko wrote: > > > I have to think about it some more (the brain is not working anymore > > > today). But what we really need is that nobody gets the same id while > > > the css is alive. So css_from_id returning NULL doesn't seem to be > > > enough. > > > > Oh, I meant whether it's necessary to keep css_from_id() working > > (ie. doing successful lookups) between offline and release, because > > that's where lifetimes are coupled. IOW, if it's enough for cgroup to > > not recycle the ID until all css's are released && fail css_from_id() > > lookup after the css is offlined, I can make a five liner quick fix. > > Don't take my word on it, I'm too fuzzy on this: but although it would > be good to refrain from recycling the ID until all css's are released, > I believe that it would not be good enough to fail css_from_id() once > the css is offlined - mem_cgroup_uncharge_swap() needs to uncharge the > hierarchy of the dead memcg (for example, when tmpfs file is removed). > > Uncharging the dead memcg itself is presumably irrelevant, but it does > need to locate the right parent to uncharge, and NULL css_from_id() > would make that impossible. Exactly! -- 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>