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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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <57c5f44f-3921-478b-843b-877fae536591@kernel.org> X-Rspamd-Queue-Id: C89A91C0009 X-Stat-Signature: e97tqkymmpgjxtxa5cisphcxa1dch3ch X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1769129021-90306 X-HE-Meta: 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 akDeQU9i rz9r6H+vFNaiTXysjAR+rULKNpkDxELTFWyRbjc/rs6u9xuIGE7GS3EZGIJCHp5e1YmIxMeU6hN3gARU/Wr8IvQnjnDdB6TiqV+++VeYy3/uXMhHeWHMAjEBk+ZOz1SDvdpBuolz5F/N1TdGgytD8PHLqaJieXAEpmOYnrfddvoqh/W6PsgpxvN/FW1akm4D1FVm7R1pmyp8OzVm7uf84Fo4NmhJi2KyWz56Y3wDKbL685d8Cf6n5l891L/W8whDDZZ3BniA8L83W1Ms/p/dL48Y6CUe/zLDw2/DV4KhieTrDEN3j9htOpyzZlbsuBI3txp20AQhYd6ug2Rg= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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