From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E4FFCC3A5A6 for ; Sun, 22 Sep 2019 22:32:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BE0D1206B6 for ; Sun, 22 Sep 2019 22:32:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388679AbfIVWcl (ORCPT ); Sun, 22 Sep 2019 18:32:41 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:34961 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729612AbfIVWck (ORCPT ); Sun, 22 Sep 2019 18:32:40 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out03.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1iC9bB-00016O-4Z; Sun, 22 Sep 2019 15:40:53 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1iC9bA-0006lK-5E; Sun, 22 Sep 2019 15:40:52 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Heinrich Schuchardt Cc: Michal Hocko , Andrew Morton , LKML References: <20190917100350.GB1872@dhcp22.suse.cz> <38349607-b09c-fa61-ccbb-20bee9f282a3@gmx.de> <20190917153830.GE1872@dhcp22.suse.cz> <87ftku96md.fsf@x220.int.ebiederm.org> <20190918071541.GB12770@dhcp22.suse.cz> <87h8585bej.fsf@x220.int.ebiederm.org> <20190922065801.GB18814@dhcp22.suse.cz> Date: Sun, 22 Sep 2019 16:40:26 -0500 In-Reply-To: (Heinrich Schuchardt's message of "Sun, 22 Sep 2019 17:31:16 +0200") Message-ID: <875zlk2enp.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1iC9bA-0006lK-5E;;;mid=<875zlk2enp.fsf@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+dpU+wrMcpwUJyGndmWILCcP3mbhZWntQ= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: threads-max observe limits X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Heinrich Schuchardt writes: > Did this patch when applied to the customer's kernel solve any problem? > > WebSphere MQ is a messaging application. If it hits the current limits > of threads-max, there is a bug in the software or in the way that it has > been set up at the customer. Instead of messing around with the kernel > the application should be fixed. While it is true that almost every workload will be buggy if it exceeds 1/8 of memory with just the kernel data structures for threads. It is not necessary true of every application. I can easily imagine cases up around 1/2 of memory where things could work reasonably. Further we can exhaust all of memory much more simply in a default configuration by malloc'ing more memory that in physically present and zeroing it all. Henrich, you were the one messed with the kernel by breaking a reasonable kernel tunable. AKA you caused a regression. That violates the no regression rule. As much as possible we fix regressions so software that used to work continues to work. Removing footguns is not a reason to introduce a regression. I do agree that Michal's customer's problem sounds like it is something else but if the kernel did not have a regression we could focus on the real problem instead of being side tracked by the regression. > With this patch you allow administrators to set values that will crash > their system. And they will not even have a way to find out the limits > which he should adhere to. So expect a lot of systems to be downed > this way. Nope. The system administrator just setting a higher value whon't crash their system. Only using that many resources would crash the system. Nor is a sysctl like this for discovering the physical limits of a machine. Which the current value is vastly inappropriate for. As the physical limits of many machines are much higher than 1/8 of memory. Eric