On Wed, Nov 21, 2012 at 12:27:28PM +0400, Glauber Costa wrote: > On 11/20/2012 10:23 PM, David Rientjes wrote: > > Anton can correct me if I'm wrong, but I certainly don't think this is > > where mempressure is headed: I don't think any accounting needs to be done Yup, I'd rather not do any accounting, at least not in bytes. > > and, if it is, it's a design issue that should be addressed now rather > > than later. I believe notifications should occur on current's mempressure > > cgroup depending on its level of reclaim: nobody cares if your memcg has a > > limit of 64GB when you only have 32GB of RAM, we'll want the notification. > > My main concern is that to trigger those notifications, one would have > to first determine whether or not the particular group of tasks is under > pressure. As far as I understand, the notifications will be triggered by a process that tries to allocate memory. So, effectively that would be a per-process pressure. So, if one process in a group is suffering, we notify that "a process in a group is under pressure", and the notification goes to a cgroup listener > And to do that, we need to somehow know how much memory we are > using, and how much we are reclaiming, etc. On a system-wide level, we > have this information. On a grouplevel, this is already accounted by memcg. > > In fact, the current code already seems to rely on memcg: > > + vmpressure(sc->target_mem_cgroup, > + sc->nr_scanned - nr_scanned, nr_reclaimed); Well, I'm yet unsure about the details, but I guess in "mempressure" cgroup approach, this will be derived from the current->, i.e. a task. But note that we won't report pressure to a memcg cgroup, we will notify only mempressure cgroup. But a process can be in both of them simultaneously. In the code, the mempressure and memcg will not depend on each other. > Now, let's start simple: Assume we will have a different cgroup. > We want per-group pressure notifications for that group. How would you > determine that the specific group is under pressure? If a process that tries to allocate memory & causes reclaim is a part of the cgroup, then cgroup has a pressure. At least that's very brief understanding of the idea, details to be investigated... But I welcome David to comment whether I got everything correctly. :) Thanks, Anton. -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
