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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-89491853478sm5521546d6.25.2026.01.22.16.43.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Jan 2026 16:43:40 -0800 (PST) Date: Thu, 22 Jan 2026 19:43:38 -0500 From: Gregory Price To: "David Hildenbrand (Red Hat)" Cc: linux-mm@kvack.org, linux-cxl@vger.kernel.org, nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, kernel-team@meta.com, dan.j.williams@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, mst@redhat.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, osalvador@suse.de, akpm@linux-foundation.org Subject: Re: [PATCH 7/8] dax/kmem: add sysfs interface for runtime hotplug state control Message-ID: References: <20260114085201.3222597-1-gourry@gourry.net> <20260114085201.3222597-8-gourry@gourry.net> <3555385d-23de-492c-8192-a991f91d4343@kernel.org> <57c5f44f-3921-478b-843b-877fae536591@kernel.org> 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: <57c5f44f-3921-478b-843b-877fae536591@kernel.org> On Thu, Jan 22, 2026 at 11:49:48PM +0100, David Hildenbrand (Red Hat) wrote: > > I'm merely wondering why, in the new world, you would even want the offline > state. > > So what are the use cases for that? > I don't have one, and in the 5-patch series I killed it. You are right, it makes no sense. However: > Why would user space possibly want that? [plugged-in offline blocks] > I don't think anyone does. This is baggage. The CXL driver auto-creates dax_kmem w/ offline memory blocks Changing this behavior breaks existing systems :[ > Can't ndctl just use the old (existing) interface if such an operation is > requested, and the new one (you want to add) when we want to do something > reasonable (actually use system ram? :) ). I think we're in agreement, I think I'm doing a poor job of explaining the interconnected issues. summarizing the long email: cxl/region + dax/cxl.c + dax/bus.c auto-probe baggage for BIOS-configured regions prevents any userland policy from from being plumbed from cxl to dax. There's no interposition step. So yes - new interfaces would resolve this and the old interfaces could be left for compat. ~Gregory