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=unavailable 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 3D6F4C43610 for ; Wed, 14 Nov 2018 07:49:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0DEB1223DD for ; Wed, 14 Nov 2018 07:49:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0DEB1223DD Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de 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 S1732135AbeKNRvb (ORCPT ); Wed, 14 Nov 2018 12:51:31 -0500 Received: from mx2.suse.de ([195.135.220.15]:47858 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727375AbeKNRvb (ORCPT ); Wed, 14 Nov 2018 12:51:31 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 94B85AC38; Wed, 14 Nov 2018 07:49:23 +0000 (UTC) Subject: Re: multipath-tools: add ANA support for NVMe device To: Mike Snitzer , Keith Busch , Sagi Grimberg , hch@lst.de, axboe@kernel.dk Cc: Martin Wilck , lijie , xose.vazquez@gmail.com, linux-nvme@lists.infradead.org, chengjike.cheng@huawei.com, shenhong09@huawei.com, dm-devel@redhat.com, wangzhoumengjian@huawei.com, christophe.varoqui@opensvc.com, bmarzins@redhat.com, sschremm@netapp.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <1541657381-7452-1-git-send-email-lijie34@huawei.com> <2691abf6733f791fb16b86d96446440e4aaff99f.camel@suse.com> <20181112215323.GA7983@redhat.com> <20181113161838.GC9827@localhost.localdomain> <20181113180008.GA12513@redhat.com> <20181114053837.GA15086@redhat.com> From: Hannes Reinecke Message-ID: <30cf7af7-8826-55bd-e39a-4f81ed032f6d@suse.de> Date: Wed, 14 Nov 2018 08:49:23 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: <20181114053837.GA15086@redhat.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 11/14/18 6:38 AM, Mike Snitzer wrote: > On Tue, Nov 13 2018 at 1:00pm -0500, > Mike Snitzer wrote: > >> On Tue, Nov 13 2018 at 11:18am -0500, >> Keith Busch wrote: >> >>> On Mon, Nov 12, 2018 at 04:53:23PM -0500, Mike Snitzer wrote: >>>> On Mon, Nov 12 2018 at 11:23am -0500, >>>> Martin Wilck wrote: >>>> >>>>> Hello Lijie, >>>>> >>>>> On Thu, 2018-11-08 at 14:09 +0800, lijie wrote: >>>>>> Add support for Asynchronous Namespace Access as specified in NVMe >>>>>> 1.3 >>>>>> TP 4004. The states are updated through reading the ANA log page. >>>>>> >>>>>> By default, the native nvme multipath takes over the nvme device. >>>>>> We can pass a false to the parameter 'multipath' of the nvme-core.ko >>>>>> module,when we want to use multipath-tools. >>>>> >>>>> Thank you for the patch. It looks quite good to me. I've tested it with >>>>> a Linux target and found no problems so far. >>>>> >>>>> I have a few questions and comments inline below. >>>>> >>>>> I suggest you also have a look at detect_prio(); it seems to make sense >>>>> to use the ana prioritizer for NVMe paths automatically if ANA is >>>>> supported (with your patch, "detect_prio no" and "prio ana" have to be >>>>> configured explicitly). But that can be done in a later patch. >>>> >>>> I (and others) think it makes sense to at least triple check with the >>>> NVMe developers (now cc'd) to see if we could get agreement on the nvme >>>> driver providing the ANA state via sysfs (when modparam >>>> nvme_core.multipath=N is set), like Hannes proposed here: >>>> http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html >>>> >>>> Then the userspace multipath-tools ANA support could just read sysfs >>>> rather than reinvent harvesting the ANA state via ioctl. >>> >>> I'd prefer not duplicating the log page parsing. Maybe nvme's shouldn't >>> even be tied to CONFIG_NVME_MULTIPATH so that the 'multipath' param >>> isn't even an issue. >> >> I like your instincts, we just need to take them a bit further. >> >> Splitting out the kernel's ANA log page parsing won't buy us much given >> it is userspace (multipath-tools) that needs to consume it. The less >> work userspace needs to do (because kernel has already done it) the >> better. >> >> If the NVMe driver is made to always track and export the ANA state via >> sysfs [1] we'd avoid userspace parsing duplication "for free". This >> should occur regardless of what layer is reacting to the ANA state >> changes (be it NVMe's native multipathing or multipath-tools). >> >> ANA and NVMe multipathing really are disjoint, making them tightly >> coupled only serves to force NVMe driver provided multipathing _or_ >> userspace ANA state tracking duplication that really isn't ideal [2]. >> >> We need a reasoned answer to the primary question of whether the NVMe >> maintainers are willing to cooperate by providing this basic ANA sysfs >> export even if nvme_core.multipath=N [1]. >> >> Christoph said "No" [3], but offered little _real_ justification for why >> this isn't the right thing for NVMe in general. > ... >> [1]: http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html >> [2]: https://www.redhat.com/archives/dm-devel/2018-November/msg00072.html > ... > > I knew there had to be a pretty tight coupling between the NVMe driver's > native multipathing and ANA support... and that the simplicity of > Hannes' patch [1] was too good to be true. > > The real justification for not making Hannes' change is it'd effectively > be useless without first splitting out the ANA handling done during NVMe > request completion (NVME_SC_ANA_* cases in nvme_failover_req) that > triggers re-reading the ANA log page accordingly. > > So without the ability to drive the ANA workqueue to trigger > nvme_read_ana_log() from the nvme driver's completion path -- even if > nvme_core.multipath=N -- it really doesn't buy multipath-tools anything > to have the NVMe driver export the ana state via sysfs, because that ANA > state will never get updated. > Hmm. Indeed, I was more focussed on having the sysfs attributes displayed, so yes, indeed it needs some more work. >> The inability to provide proper justification for rejecting a patch >> (that already had one co-maintainer's Reviewed-by [5]) _should_ render >> that rejection baseless, and the patch applied (especially if there is >> contributing subsystem developer interest in maintaining this support >> over time, which there is). At least that is what would happen in a >> properly maintained kernel subsystem. >> >> It'd really go a long way if senior Linux NVMe maintainers took steps to >> accept reasonable changes. > > Even though I'm frustrated I was clearly too harsh and regret my tone. > I promise to _try_ to suck less. > > This dynamic of terse responses or no responses at all whenever NVMe > driver changes to ease multipath-tools NVMe support are floated is the > depressing gift that keeps on giving. But enough excuses... > > Not holding my breath BUT: > if decoupling the reading of ANA state from native NVMe multipathing > specific work during nvme request completion were an acceptable > advancement I'd gladly do the work. > I'd be happy to work on that, given that we'll have to have 'real' ANA support for device-mapper anyway for SLE12 SP4 etc. Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@suse.de +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg)