From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755460AbdJLVsj (ORCPT ); Thu, 12 Oct 2017 17:48:39 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:46532 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750990AbdJLVsh (ORCPT ); Thu, 12 Oct 2017 17:48:37 -0400 Date: Thu, 12 Oct 2017 22:47:42 +0100 From: Roman Gushchin To: Peter Zijlstra CC: , Tejun Heo , Oleg Nesterov , Linus Torvalds , Andrew Morton , Thomas Gleixner , Chris Mason , Subject: Re: [RFC 1/2] cgroup, kthread: do not allow moving kthreads out of the root cgroup Message-ID: <20171012214742.GA18254@castle> References: <20171012173723.13381-1-guro@fb.com> <20171012192445.xdyrueypbncvappq@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20171012192445.xdyrueypbncvappq@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.1 (2017-09-22) X-Originating-IP: [2620:10d:c092:180::1:f81b] X-ClientProxiedBy: HE1PR0402CA0007.eurprd04.prod.outlook.com (2603:10a6:3:d0::17) To DM3PR15MB1081.namprd15.prod.outlook.com (2603:10b6:0:12::7) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: ccff94bb-8117-4de5-f84e-08d511bae7bc X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(22001)(2017030254152)(2017052603199)(201703131423075)(201703031133081)(201702281549075);SRVR:DM3PR15MB1081; 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Kernel threads are generally performing the work required > > to keep the system working and healthy, and applying various > > resource limits may affect system stability and performance. > > > > Some examples of dangerous behavior are limiting CPU time available > > to rcu stuff, memory limits applied to almost all kthreads, etc. > > > > To prevent this dangerous behavior, let's deny all kthread > > movements between cgroups. Right now only kthreads bounded > > to CPUs are not allowed to move, which is not sufficient. > > > > If there are examples of kthreads which can be limited, > > and it's guaranteed to be safe, we can allow explicit > > exceptions further. > > The traditional use-case is stuffing all the unbound kthreads into a > system cpuset in order to limit 'crap' on the rest of the CPUs. > This setup is typically found in HPC and RT environments. > > So NAK. This needs to stay working in as far as it still works. Ok, thanks!