From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx123.postini.com [74.125.245.123]) by kanga.kvack.org (Postfix) with SMTP id 34A0D6B0085 for ; Wed, 21 Nov 2012 03:49:16 -0500 (EST) Received: by mail-pb0-f41.google.com with SMTP id xa7so5286075pbc.14 for ; Wed, 21 Nov 2012 00:49:15 -0800 (PST) Date: Wed, 21 Nov 2012 00:46:03 -0800 From: Anton Vorontsov Subject: Re: [RFC v3 0/3] vmpressure_fd: Linux VM pressure notifications Message-ID: <20121121084603.GA18159@lizard> References: <20121115085224.GA4635@lizard> <50A60873.3000607@parallels.com> <50A6AC48.6080102@parallels.com> <50AA3FEF.2070100@parallels.com> <50AC9070.2030009@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <50AC9070.2030009@parallels.com> Sender: owner-linux-mm@kvack.org List-ID: To: Glauber Costa Cc: David Rientjes , "Kirill A. Shutemov" , Pekka Enberg , Mel Gorman , Leonid Moiseichuk , KOSAKI Motohiro , Minchan Kim , Bartlomiej Zolnierkiewicz , John Stultz , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linaro-kernel@lists.linaro.org, patches@linaro.org, kernel-team@android.com, linux-man@vger.kernel.org, KAMEZAWA Hiroyuki , Michal Hocko , Johannes Weiner , Tejun Heo 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org