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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-890772674fdsm161880336d6.47.2026.01.12.16.09.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Jan 2026 16:09:14 -0800 (PST) Date: Mon, 12 Jan 2026 19:08:40 -0500 From: Gregory Price To: Anisa Su Cc: dan.j.williams@intel.com, Ira Weiny , dave@stgolabs.net, linux-cxl@vger.kernel.org, nifan.cxl@gmail.com, dongjoo.seo1@samsung.com Subject: Re: [RFC PATCH 0/3] Add Support for Multiple DC Regions Message-ID: References: <20251203203540.1091827-1-anisa.su887@gmail.com> <6931c4c85a526_43de3100bb@iweiny-mobl.notmuch> <693cdf385657a_2e71710083@dwillia2-mobl4.notmuch> Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Jan 12, 2026 at 02:50:01PM -0800, Anisa Su wrote: > On Sat, Dec 13, 2025 at 12:36:24PM +0900, dan.j.williams@intel.com wrote: > > Anisa Su wrote: > > [..] > > > > Unfortunately none of the details presented in this cover letter really > > > > show why the kernel needs this additional complexity. > > > > > > > > Can you go into more details on the use cases of multiple partitions? > > > > > > > From what I understand, the motivation for DCD as a whole has always been a > > > blocker for the entire series. However, this year we've seen multiple vendors > > > demo memory pooling/sharing at SC,25[1], as well as the development of a > > > controller that supports "memory pooling and sharing across > > > multiple hosts" from Montage[2]. > > > > > > The flexibility and control provided by multiple partitions is > > > an important capability of DCD for enabling composable memory > > > infrastructures. IMO, adding multi-partition support back in from v8 or > > > picking up this patchset would strengthen the series. > > > > Can you explain the use case for multiple partitions per-device? > > Describe it in terms of what Linux loses if it never entertains this > > aspect of the specification. It significantly complicates the ABI for a > > benefit to Linux that I am unable to articulate. > > Let me backtrack a bit here :( I was too hasty trying to push for > multiple partitions. > > However, can I ask for some clarification on what a sufficient use case is > (with just a single partition)? > > Then I'll (try my best) to demonstrate how this series can accomplish it > so I can help land the single partition stuff first. Does that sound fair > to you? Or am I misunderstanding the core problem? > > Thanks, > Anisa regions != partitions the discussion from today was regarding FAMFS wanting to balance over subscription and max bandwidth - which requires a per-device region and an interleaved regions, they cannot be managed with one region. I can't think of a reason to need multiple *physical partitions* on the device, when you can chop up a single partition with many regions. Either way you need dedicated decoders for each region - regardless of what partition it's on, so the extra partition doesn't get you much. ~Gregory