Hello, Li. On Wed, May 14, 2014 at 12:21:25PM +0800, Li Zefan wrote: > > There are now use cases where controllers need to iterate through > > csses regardless of their online state as long as they have positive > > What use cases are we talking about here? memcg wants to be able to iterate all csses whose refcnts haven't reached zero yet so that it can treat offline csses the same way as online ones in terms of memory reclaim. They don't contain new tasks so new charges won't be created but offlining won't try to transfer all charges to the parent but just leave the offline child attached until all charges are eventually reclaimed from the pressure from the parent. I'm not too familiar with the details but this makes sense in generic sense too. Offline marks an object starting its draining phase and release marks the actual destruction point. For controllers with persistent states like memcg, it's a lot more natural to deal offlined csses as "active but draining following the usual hierarchical operation" rather than trying to explicitly update the states from offline to move them to the parent especially as the effort there essentially is a waste as most of those moved charges aren't gonna be used in the parent and will be released eventually. Guaranteeing iteration of offline but not-released csses allow controllers to treat the draining stage between offline and release more or less identically to online state which in turn can make ->css_offline() significantly simpler and lighter. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
