From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [RFC] cgroup TODOs Date: Fri, 14 Sep 2012 12:44:39 -0700 Message-ID: <20120914194439.GP17747@google.com> References: <20120913205827.GO7677@google.com> <20120914180754.GF6221@redhat.com> <20120914185324.GI17747@google.com> <20120914192840.GG6221@redhat.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=0oYN/5joobugnGAdjQZ+qEN6YrFYK50y27dJC/xSND4=; b=XlHiceML7k+JJeIJsLNbS/UCzgfeqWOdti3qaQStJRfKt5KJEznR2bfWTYMKZrfrJV McKF8Mia2B6eox0IdRdOyhwukactE4LUcO/xYCttAdH53j6OhKrRWMHOMATNjrK/z14u 3hVb1WVI2IM+rUi4srBKgOH2nCj3TqW89GlbTF59mPk4gVD9HLSqIe20YXDa6DFQj8LL 0ogrQskaa3RCAmtyOnh6A88XjyFof93JYlw6XuhHnqEMQNTrzqLwpIJ5WkNlnFtW3l30 7WoKVyqn5V5py6tLiWRnYZndGUzbIKuKNCjQZyI1dgCtOfzocmiM0V9lUQY4hKnaxRtF LJFg== Content-Disposition: inline In-Reply-To: <20120914192840.GG6221-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Vivek Goyal Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Li Zefan , Michal Hocko , Glauber Costa , Peter Zijlstra , Paul Turner , Johannes Weiner , Thomas Graf , Paul Mackerras , Ingo Molnar , Arnaldo Carvalho de Melo , Neil Horman , "Aneesh Kumar K.V" , Serge Hallyn Hello, Vivek. On Fri, Sep 14, 2012 at 03:28:40PM -0400, Vivek Goyal wrote: > Hmm.., In that case how libvirt will make use of blkio in the proposed > scheme. We can't disable blkio nesting at "system" level. So We will > have to disable it at each service level except "libvirtd" so that > libvirt can use blkio for its virtual machines. > > That means blkio will see each service in a cgroup of its own and if > that does not make sense by default, its a problem. In the existing Yeap, if libvirtd wants use blkcg, blkcg will be enabled upto libvirtd's root. It might not be optimal but I think it makes sense. If you want to excercise hierarchical control on a resource, the only sane way is sticking to the hierarchy until it reaches root. > scheme, atleast every service does not show up in its cgroup from > blkio point of view. Everthig is in root and libvirt can create its > own cgroups, keeping number of cgroups small. Even a broken clock is right twice a day. I don't think this is a behavior we can keep for the sake of "but if we do this ass-weird thing, we can bypass the overhead for XYZ" when it breaks so many fundamental things. I think there currently is too much (broken) flexibility and intent to remove it. That doesn't mean that removeing all flexibility is the right direction. It inherently is a balancing act and I think the proposed solution is a reasonable tradeoff. There's important difference between causing full overhead by default for all users and requiring some overhead when the use case at hand calls for the functionality. Thanks. -- tejun From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932411Ab2INToq (ORCPT ); Fri, 14 Sep 2012 15:44:46 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:48313 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932354Ab2INToo (ORCPT ); Fri, 14 Sep 2012 15:44:44 -0400 Date: Fri, 14 Sep 2012 12:44:39 -0700 From: Tejun Heo To: Vivek Goyal Cc: containers@lists.linux-foundation.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Li Zefan , Michal Hocko , Glauber Costa , Peter Zijlstra , Paul Turner , Johannes Weiner , Thomas Graf , Paul Mackerras , Ingo Molnar , Arnaldo Carvalho de Melo , Neil Horman , "Aneesh Kumar K.V" , Serge Hallyn Subject: Re: [RFC] cgroup TODOs Message-ID: <20120914194439.GP17747@google.com> References: <20120913205827.GO7677@google.com> <20120914180754.GF6221@redhat.com> <20120914185324.GI17747@google.com> <20120914192840.GG6221@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120914192840.GG6221@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Vivek. On Fri, Sep 14, 2012 at 03:28:40PM -0400, Vivek Goyal wrote: > Hmm.., In that case how libvirt will make use of blkio in the proposed > scheme. We can't disable blkio nesting at "system" level. So We will > have to disable it at each service level except "libvirtd" so that > libvirt can use blkio for its virtual machines. > > That means blkio will see each service in a cgroup of its own and if > that does not make sense by default, its a problem. In the existing Yeap, if libvirtd wants use blkcg, blkcg will be enabled upto libvirtd's root. It might not be optimal but I think it makes sense. If you want to excercise hierarchical control on a resource, the only sane way is sticking to the hierarchy until it reaches root. > scheme, atleast every service does not show up in its cgroup from > blkio point of view. Everthig is in root and libvirt can create its > own cgroups, keeping number of cgroups small. Even a broken clock is right twice a day. I don't think this is a behavior we can keep for the sake of "but if we do this ass-weird thing, we can bypass the overhead for XYZ" when it breaks so many fundamental things. I think there currently is too much (broken) flexibility and intent to remove it. That doesn't mean that removeing all flexibility is the right direction. It inherently is a balancing act and I think the proposed solution is a reasonable tradeoff. There's important difference between causing full overhead by default for all users and requiring some overhead when the use case at hand calls for the functionality. Thanks. -- tejun