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Wed, 24 Sep 2025 01:16:07 +0000 From: Date: Tue, 23 Sep 2025 18:16:05 -0700 To: =?UTF-8?B?TWljaGHFgiBDxYJhcGnFhHNraQ==?= , "Mike Rapoport" CC: Ira Weiny , Dan Williams , Dave Jiang , Vishal Verma , , Pasha Tatashin , "Tyler Hicks" , , Message-ID: <68d3465541f82_105201005@dwillia2-mobl4.notmuch> In-Reply-To: References: <20250826080430.1952982-1-rppt@kernel.org> <20250826080430.1952982-2-rppt@kernel.org> <68b0f8a31a2b8_293b3294ae@iweiny-mobl.notmuch> Subject: Re: [PATCH 1/1] nvdimm: allow exposing RAM carveouts as NVDIMM DIMM devices Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: SJ0PR03CA0377.namprd03.prod.outlook.com (2603:10b6:a03:3a1::22) To PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR11MB8107:EE_|CH8PR11MB9505:EE_ X-MS-Office365-Filtering-Correlation-Id: c9836c32-e6d5-4ab7-800c-08ddfb07f012 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016; 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I do wonder if the use cases are the same? > > > > They are mutually exclusive in the sense that they cannot be loaded > > together so I had this in Kconfig in RFC posting > > > > config RAMDAX > > tristate "Support persistent memory interfaces on RAM carveouts= " > > depends on OF || (X86 && X86_PMEM_LEGACY=3Dn) > > > > (somehow my rebase lost Makefile and Kconfig changes :( ) > > > > As Pasha said in the other thread [1] the use-cases are different. My g= oal > > is to achieve flexibility in managing carved out "PMEM" regions and > > Michal's patches aim to optimize boot time by autoconfiguring multiple = PMEM > > regions in the kernel without upcalls to ndctl. > > > > > From a high level I don't like the idea of adding kernel parameters. = So > > > if this could solve Michal's problem I'm inclined to go this directio= n. > > > > I think it could help with optimizing the reboot times. On the first bo= ot > > the PMEM is partitioned using ndctl and then the partitioning remains t= here > > so that on subsequent reboots kernel recreates dax devices without upca= lls > > to userspace. >=20 > Using this patch, if I want to divide 500GB of memory into 1GB chunks, > the last 128kB of every chunk would be taken by the label, right? >=20 > My patch disables labels, so we can divide the memory into 1GB chunks > without any losses and they all remain aligned to the 1GB boundary. I > think this is necessary for vmemmap dax optimization. As Mike says you would lose 128K at the end, but that indeed becomes losing that 1GB given alignment constraints. However, I think that could be solved by just separately vmalloc'ing the label space for this. Then instead of kernel parameters to sub-divide a region, you just have an initramfs script to do the same. Does that meet your needs?=