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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 6698EC43382 for ; Tue, 25 Sep 2018 22:28:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0B47E20867 for ; Tue, 25 Sep 2018 22:28:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0B47E20867 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.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 S1726171AbeIZEht (ORCPT ); Wed, 26 Sep 2018 00:37:49 -0400 Received: from mga05.intel.com ([192.55.52.43]:18709 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725762AbeIZEht (ORCPT ); Wed, 26 Sep 2018 00:37:49 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 25 Sep 2018 15:28:05 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,303,1534834800"; d="scan'208";a="94780930" Received: from ahduyck-mobl.amr.corp.intel.com (HELO [10.7.198.152]) ([10.7.198.152]) by orsmga002.jf.intel.com with ESMTP; 25 Sep 2018 15:27:59 -0700 Subject: Re: [PATCH v5 2/4] mm: Provide kernel parameter to allow disabling page init poisoning To: Dave Hansen , linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org Cc: pavel.tatashin@microsoft.com, mhocko@suse.com, dave.jiang@intel.com, jglisse@redhat.com, rppt@linux.vnet.ibm.com, dan.j.williams@intel.com, logang@deltatee.com, mingo@kernel.org, kirill.shutemov@linux.intel.com References: <20180925200551.3576.18755.stgit@localhost.localdomain> <20180925201921.3576.84239.stgit@localhost.localdomain> <13285e05-fb90-b948-6f96-777f94079657@intel.com> <8faf3acc-e47e-8ef9-a1a0-c0d6ebfafa1e@linux.intel.com> <75dde720-c997-51a4-d2e2-8b08eb201550@intel.com> From: Alexander Duyck Message-ID: <61358149-b233-6194-adcf-2c16b9112fd7@linux.intel.com> Date: Tue, 25 Sep 2018 15:27:59 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <75dde720-c997-51a4-d2e2-8b08eb201550@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/25/2018 3:14 PM, Dave Hansen wrote: > On 09/25/2018 01:38 PM, Alexander Duyck wrote: >> On 9/25/2018 1:26 PM, Dave Hansen wrote: >>> On 09/25/2018 01:20 PM, Alexander Duyck wrote: >>>> +    vm_debug[=options]    [KNL] Available with CONFIG_DEBUG_VM=y. >>>> +            May slow down system boot speed, especially when >>>> +            enabled on systems with a large amount of memory. >>>> +            All options are enabled by default, and this >>>> +            interface is meant to allow for selectively >>>> +            enabling or disabling specific virtual memory >>>> +            debugging features. >>>> + >>>> +            Available options are: >>>> +              P    Enable page structure init time poisoning >>>> +              -    Disable all of the above options >>> >>> Can we have vm_debug=off for turning things off, please?  That seems to >>> be pretty standard. >> >> No. The simple reason for that is that you had requested this work like >> the slub_debug. If we are going to do that then each individual letter >> represents a feature. That is why the "-" represents off. We cannot have >> letters represent flags, and letters put together into words. For >> example slub_debug=OFF would turn on sanity checks and turn off >> debugging for caches that would have causes higher minimum slab orders. > > We don't have to have the same letters mean the same things for both > options. We also can live without 'o' and 'f' being valid. We can > *also* just say "don't do 'off'" if you want to enable things. I'm not saying we do either. I would prefer it if we stuck to similar behavior though. If we are going to do a slub_debug style parameter then we should stick with similar behavior where "-" is used to indicate all features off. > I'd much rather have vm_debug=off do the right thing than have > per-feature enable/disable. I know I'll *never* remember vm_debug=- and > doing it this way will subject me to innumerable trips to Documentation/ > during my few remaining years. > > Surely you can make vm_debug=off happen. :) I could, but then it is going to confuse people even more. I really feel that if we want to do a slub_debug style interface we should use the same switch for turning off all the features that they do for slub_debug. >>> we need to document the defaults.  I think the default is "all >>> debug options are enabled", but it would be nice to document that. >> >> In the description I call out "All options are enabled by default, and this interface is meant to allow for selectively enabling or disabling". > > I found "all options are enabled by default" really confusing. Maybe: > > "Control debug features which become available when CONFIG_DEBUG_VM=y. > When this option is not specified, all debug features are enabled. Use > this option enable a specific subset." > > Then, let's actually say what the options do, and what their impact is: > > P Enable 'struct page' poisoning at initialization. > (Slows down boot time). > From my perspective I just don't see how this changes much since it conveys the same message I had conveyed in my description. Since it looks like Andrew applied the patch feel free to submit your suggestion here as a follow-up patch and I would be willing to review/ack it.