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Fri, 22 Nov 2024 12:49:38 -0500 X-MC-Unique: nUFJHOxpOkKCm9DDV94noA-1 X-Mimecast-MFC-AGG-ID: nUFJHOxpOkKCm9DDV94noA Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 269E719560AA; Fri, 22 Nov 2024 17:49:37 +0000 (UTC) Received: from [10.22.81.129] (unknown [10.22.81.129]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id BD8D630000DF; Fri, 22 Nov 2024 17:49:33 +0000 (UTC) Message-ID: Date: Fri, 22 Nov 2024 12:49:32 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] nvme: always enable multipath To: Keith Busch , Christoph Hellwig Cc: Bryan Gurney , linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, sagi@grimberg.me, axboe@kernel.dk, mpe@ellerman.id.au, naveen@kernel.org, maddy@linux.ibm.com, kernel@xen0n.name, bmarzins@redhat.com References: <20241121220321.40616-1-bgurney@redhat.com> <20241122120925.GA25817@lst.de> Content-Language: en-US From: John Meneghini Organization: RHEL Core Storge Team In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241122_094944_814975_629A6F8E X-CRM114-Status: GOOD ( 24.29 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On 11/22/24 10:39, Keith Busch wrote: > On Fri, Nov 22, 2024 at 01:09:25PM +0100, Christoph Hellwig wrote: >> On Thu, Nov 21, 2024 at 05:03:21PM -0500, Bryan Gurney wrote: >>> Since device-mapper multipath will no longer be operating on NVMe >>> devices, there is no longer a need to set CONFIG_NVME_MULTIPATH=n. >>> >>> Always enable NVMe multipath, remove CONFIG_NVME_MULTIPATH, and use >>> the code paths that would be used if CONFIG_NVME_MULTIPATH=y. >> >> As mentioned last round not having to build the not tiny multipath >> code for embedded systems and other small builds that never require >> multipathing still seems like a sensible idea. > > It's not just embedded either. I have plenty of single port datacenter > PCIe NVMe's that claim multi-controller capabilities. I think it's some > artifact of SRIOV that some versions of the firmware can bring. > > Anyway, we only use the one physical function, so they're certainly not > multipath devices here. We disable the CONFIG option because while the > nvme multipath IO overhead is low, it's not zero. So you're saying you want to keep CONFIG_NVME_MULTIPATH and simply remove the modparam nvme_core.multipath? (I know I said we were going to do that but that's before Bryan and I started testing his changes with blktests. I think we can fix that.) The problem with this solution is: when you build a kernel with CONFIG_NVME_MULTIPATH=n you get exactly the same thing as CONFIG_NVME_MULTIPATH=y with nvme_core.multipath=n. You get a separate /dev/nvmeNN entry for every namespace/controller path, minus the multipath.c code. So, I don't see the point. If you really want to stop supporting user space multi-path solutions like DMMP with nvme we need to stop creating multiple dev entries for multi-path controllers, no matter what. Note that this multi-pathing stuff is a part of the confusion in UDEV, like I spoke about at ALPPS this year. One reason why the /dev/disk/by-path symlinks are so broken is because the kernel has at least three different ways to configure multi-pathing support for nvme devices. We've been saying we're going to do this since since v5.18. So how do we want to do this? - - if (!multipath) { - dev_warn(ctrl->device, - "Found shared namespace %d, but multipathing not supported.\n", - info->nsid); - dev_warn_once(ctrl->device, - "Support for shared namespaces without CONFIG_NVME_MULTIPATH is deprecated and will be removed in Linux 6.0.\n"); - } commit ce8d78616a6b637d1b763eb18e32045687a84305 Author: Christoph Hellwig Date: Tue Mar 15 13:27:07 2022 +0100 nvme: warn about shared namespaces without CONFIG_NVME_MULTIPATH Start warning about exposing a namespace as multiple block devices, and set a fixed deprecation release. Signed-off-by: Christoph Hellwig Reviewed-by: Keith Busch (master) > git name-rev --tags --name-only ce8d78616a6b637d1b763eb18e32045687a84305 nvme-5.18-2022-03-17^0