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Wed, 19 Feb 2025 14:47:26 +0000 (GMT) Message-ID: <2ff87386-c6db-4f2e-be91-213504d99a78@linux.ibm.com> Date: Wed, 19 Feb 2025 20:17:25 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] nvme: remove multipath module parameter To: Keith Busch , John Meneghini Cc: hch@lst.de, sagi@grimberg.me, bmarzins@redhat.com, Bryan Gurney , linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, Marco Patalano , axboe@kernel.dk References: <20250204211158.43126-1-bgurney@redhat.com> <7c588344-f019-4939-8a93-0a450481d4bc@redhat.com> <8a1730a1-1faf-4722-99e1-c3a85257b6f4@redhat.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 5sDdhRf2rzB5W1cUsG7tc1BiCsSpIlov X-Proofpoint-GUID: 5sDdhRf2rzB5W1cUsG7tc1BiCsSpIlov X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-02-19_06,2025-02-19_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 lowpriorityscore=0 suspectscore=0 clxscore=1011 bulkscore=0 malwarescore=0 phishscore=0 mlxlogscore=999 adultscore=0 impostorscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2502100000 definitions=main-2502190115 On 2/18/25 10:45 PM, Keith Busch wrote: > On Tue, Feb 18, 2025 at 11:31:58AM -0500, John Meneghini wrote: >> On 2/18/25 10:06 AM, Keith Busch wrote: >>> On Thu, Feb 13, 2025 at 03:37:28PM -0500, John Meneghini wrote: >>>> Keith, Christoph and Sagi, >>>> >>>> This patch has been fully tested and analyzed by Red Hat's QA group and no >>>> unexpected side effects or regressions have been found. Both NVMe/FC and NVMe/TCP >>>> have been tested. Our QE engineer has asked me to report this upstream. >>> >>> What's the harm in leaving the parameter? *I* use it so I can test both >>> ways without needing to compile multiple kernels. >> >> LOL. We've been talking about this since 2017. The goal has always been to remove support for DMMP with NVMe. > > I understand that disabling nvme native mp it is required for device > mapper, and I get you want to prevent the possibility of anyone using > dm-mp with nvme, but that isn't the only user that wants to see all > namespace paths. > Agreed! I do have nvme multi-controller disks and I toggle multipath module parameter to test it both ways. One with each individual path to a shared namespace and another with a single head node path and then let IO policy determine which path to choose for sending IO to disk. In fact, we have few nvme blktests which only runs if device is configured with single path and so testing it on multi-controller nvme disk would require us to turn off multipath module parameter. In that way this parameter is very handy. My typical way of toggling this parameter is: 1. disable multipath # rmmod nvme # rmmod nvme_core # modprobe nvme_core multipath=0 # modprobe nvme Now I could run all nvme blktests which require us disable multipath. 2. enable multipath: # rmmod nvme # rmmmod nvme_core # modprobe nvme_core multipath=1 # modprobe nvme Now if we get away with multipath parameter then it means we have to re-compile kernel disabling CONFIG_NVME_MULTIPATH option and that's something we may want to avoid, if possible. Having said that I'm not against this patch however we certainly have users who would be using multipath parameter and taking away this parameter may break those user application. So I'm wondering why is it not possible for RedHat to let their customer know the fact that starting with RHEL-10, we don't support DMMP for NVMe device even though the multipath module parameter is present? Thanks, --Nilay