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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 E30F9C43441 for ; Mon, 19 Nov 2018 16:19:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4FD2320851 for ; Mon, 19 Nov 2018 16:19:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4FD2320851 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730055AbeKTCnn (ORCPT ); Mon, 19 Nov 2018 21:43:43 -0500 Received: from mx1.redhat.com ([209.132.183.28]:53644 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729825AbeKTCnm (ORCPT ); Mon, 19 Nov 2018 21:43:42 -0500 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4EA2530841DE; Mon, 19 Nov 2018 16:19:38 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-55.bos.redhat.com [10.18.17.55]) by smtp.corp.redhat.com (Postfix) with ESMTP id 88D5119C7B; Mon, 19 Nov 2018 16:19:37 +0000 (UTC) Subject: Re: [PATCH] debugobjects: add a new Kconfig for POOL_SIZE To: Qian Cai , Thomas Gleixner Cc: linux kernel , arnd@arndb.de, Andrew Morton , Yang Shi References: <20181118082255.1275-1-cai@gmx.us> <5939F7F3-E332-4112-861E-C6C0DF86717E@gmx.us> <44517d7f-c34f-1424-d0db-601e590c626d@redhat.com> <1542640658.12945.41.camel@gmx.us> From: Waiman Long Openpgp: preference=signencrypt Autocrypt: addr=longman@redhat.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <1542640658.12945.41.camel@gmx.us> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Mon, 19 Nov 2018 16:19:38 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/19/2018 10:17 AM, Qian Cai wrote: > On Mon, 2018-11-19 at 09:51 -0500, Waiman Long wrote: >> On 11/19/2018 08:27 AM, Qian Cai wrote: >>> On 11/19/18 at 3:09 AM, Thomas Gleixner wrote: >>> >>>> Qian, >>>> >>>> On Sun, 18 Nov 2018, Qian Cai wrote: >>>>>> On Nov 18, 2018, at 1:21 PM, Thomas Gleixner >>>>>> wrote: >>>>>> On Sun, 18 Nov 2018, Qian Cai wrote: >>>>>>> As the results, systems have 60+ CPUs with both timer and workqueue >>>>>>> objects enabled could trigger "ODEBUG: Out of memory. ODEBUG >>>>>>> disabled". >>>>>>> >>>>>>> Hence, add a new Kconfig option so users could adjust >>>>>>> ODEBUG_POOL_SIZE >>>>>>> accordingly if either timer or workqueue objects are selected. >>>>>> why do we need a config option, when the required number can be >>>>>> deduced >>>>>> already from the active CONFIG_DEBUG_OBJECTS_* and NR_CPUS? >>>>>> >>>>> It because I am worry about the coupling between the implementation >>>>> details of >>>>> timers and workqueue objects, and the computation in the code you >>>>> mentioned >>>>> here. For example, people could change workqueue.c to have different >>>>> number >>>>> of worekqueues initialized during the early boot in the future which is >>>>> going to >>>>> affect the required pool size, and I am not sure if people are going to >>>>> adjust the >>>>> code in debugobjects.c here as well when they made changes like that. >>>>> >>>>> Also, the computation could become so complex depends on lots of config >>>>> options like perf, hrtimer, and combinations that I have not tested so >>>>> far which is >>>>> difficult to exhausted all the possibilities. >>>>> >>>>> Hence, I feel like the Kconfig option is more flexible and less error- >>>>> prone. >>>> Quite the contrary. Config options are a pain and truly error-prone if you >>>> want to compile general purpose kernels as distributions do. >>>> >>> Ah, I never thought distributions people would >>> enable those debugging options. >> Distros like RHEL usually ship two kernels - one for production and one >> for debug. The debug kernel does have debugobjects enabled. >> > Right, I can remember that now . However, if I understand correctly, since the > early static pool size needs to be determined during the compilation time, it > depends on the No. CPUs are from the machines that built the distro kernels. > Then, when users use those distro kernels, they are not going to have correct > the pool size according to the No. CPUs on their test machines. I see your point. Perhaps you can make ODEBUG_POOL_SIZE scales with CONFIG_NR_CPUS like #define ODEBUG_POOL_SIZE    (1024 + CONFIG_NR_CPUS * 2) CONFIG_NR_CPUS is usually set to a lot higher than the actual number of CPUs in a typical system. So you don't want to set the multiplier too high. Cheers, Longman