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Sat, 02 May 2026 03:48:43 -0700 (PDT) Date: Sat, 2 May 2026 11:48:41 +0100 From: Gregory Price To: Anisa Su Cc: John Groves , Davidlohr Bueso , Jonathan Cameron , Dave Jiang , Alison Schofield , Vishal Verma , Ira Weiny , Dan Williams , John Groves , Shiju Jose , Robert Richter , "linux-cxl@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "dev.srinivasulu@gmail.com" , "arramesh@micron.com" , "ajayjoshi@micron.com" Subject: Re: [RFC PATCH 0/4] cxl/extent: Enable and validate multi-extent DCDs Message-ID: References: <20260423235108.3732424-1-john@jagalactic.com> <0100019dbcc13648-596853f3-0083-46e0-b654-396eedd657cb-000000@email.amazonses.com> Precedence: bulk X-Mailing-List: linux-kernel@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 Fri, May 01, 2026 at 03:00:07PM -0700, Anisa Su wrote: > > 4. If we allow non-tagged extents (as this patchset allows): > - can non-tagged extents be partially claimed by a DAX device that > doesn't have a specified tag? > > Ira's original patchset introduced minimal changes to DAX logic. Introducing > tag-awareness to > DAX resize logic may require adding more conditional statements, > especially if we allow both NULL and non-NULL tags (but there might be a nice > way to do it; > This is just my initial impression, I haven't tried implementing it, and I could > certainly look into it more) > There is a lot of confusion built around tagged vs untagged. Can we at least agree if a DC Extent has a NULL tag: 1 extent = 1 DAX device And we just denote that a NULL UUID is a sentinel value ("Unknown"). e.g.: there's no such thing as a "partial claim by a dax device". either the extent is tagged (part of a set), or it is its own thing without any identifying data around it (probably intended to be hotplugged as system ram or something, userland problem). alternatively: do not allow untagged extents, because we can't make sense of what to do with it. ~Gregory