Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756001AbdCGTmQ (ORCPT ); Tue, 7 Mar 2017 14:42:16 -0500 Received: from mail-ot0-f175.google.com ([74.125.82.175]:35325 "EHLO mail-ot0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756086AbdCGTmG (ORCPT ); Tue, 7 Mar 2017 14:42:06 -0500 Date: Tue, 7 Mar 2017 14:41:34 -0500 From: Tejun Heo To: Krzysztof Opasiak Cc: lizefan@huawei.com, hannes@cmpxchg.org, =?utf-8?Q?=C5=81ukasz?= Stelmach , linux-kernel@vger.kernel.org, Karol Lewandowski , cgroups@vger.kernel.org Subject: Re: counting file descriptors with a cgroup controller Message-ID: <20170307194134.GE31179@htj.duckdns.org> References: <87poihtaya.fsf%l.stelmach@samsung.com> <9a57890c-d9e9-5719-e155-ce1161795a02@samsung.com> <20170306185820.GA19696@htj.duckdns.org> <7fbd9c4c-76ca-4073-9afa-1ab54364ec79@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7fbd9c4c-76ca-4073-9afa-1ab54364ec79@samsung.com> User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1345 Lines: 31 Hello, Krzysztof. On Tue, Mar 07, 2017 at 12:19:52PM +0100, Krzysztof Opasiak wrote: > So maybe let me clarify our use case so we can have some more discussion > about this. We are dealing with task of monitoring system services on an IoT > system. So this system needs to run as long as possible without reboot just > like server. In server world almost whole system state is being monitored by > services like nagios. They measure each parameter (like cpu, memory etc) > with some interval. Unfortunately we cannot use this it in an embedded > system due to power consumption. So, we don't add controllers for specific use case scenarios. The target actually has to be a fundamental resource which can't be isolated in a different way. The use case you're describing is more about working around shortcomings in userspace by implemneting a major kernel feature, when the said shortcomings can easily be controlled and mitigated from userspace - e.g. if running out of fds can't be handled reliably from the target application for some reason and the application may lock up from the condition, protect the base resources so that a monitoring process can always reliably run and let that take a corrective action when such condition is detected. This doesn't really seem to qualify as a dedicated kernel functionality. Thanks. -- tejun