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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769555223; bh=JySjp5riAZLd6mmNMgHnUjqyKf0qlSv7WXkRBVPO1CI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Vr9Fpvs6d0EEFlm4bRch6d4FLbnrB3uR9XUZB+6kxeIh5Gyst9s6dSw4NXLPzopYt XqwJV7Wnspg5pXLZXLnpM8u4tvMBkIHTJQ0Aa3TC6l4+NEAAe1TuLq2A/SZ5fW4hAk WOU1kcDPd8jgY+iJMdpEDFzhp/MyYRYBHKb4IRwaBLT+kDwRFKonaMqzzJQKkF9bnJ APJREuhAfnpqpBlGU+Rkz97qWBM2pG6xxczmOQoPtRgLSjvvmt5sCjqKuowoH188gw rNcWsvHbSVi1cMu6+i1La2I3jhMb8sceN1rhUwVuotOIbsT7MpMCO0oKxYQesQrl6P qIrKq5h/E13Ag== Message-ID: <684f11a3-1958-4562-880c-7e0afd3ae3b5@kernel.org> Date: Wed, 28 Jan 2026 00:06:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 7/8] dax/kmem: add sysfs interface for runtime hotplug state control To: Gregory Price 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 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> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: D644CA000A X-Stat-Signature: ho8wwxieg96hn13bk6ofer6xstrn74dk X-HE-Tag: 1769555224-214606 X-HE-Meta: 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 8C8+GaZ9 8r9DkvpvzfIFRDPfTDaR+m088liwvMhXuV+HYOcx8kwqi2XRqzmVbALQ/VaD+84e6Id1O8aOvPZl1INrFxgHo4o+xs/JJaj17GsDdzEY0bes9Nc9k9Wok895JrttWgSy3MTNIb6gdOjz8a7sxT3iCL7Kh2OJFzZybdn6x+N5bdeyYRI3i8CfGnCamGdxwNR1+aoTqIymb0SycCptaBjzSEtk1tcKSqhZjgChxpUY0nFdJv/gsjobZ6sM5WMxH/h2JFKa7 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 1/23/26 01:43, Gregory Price wrote: > 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. Great! -- Cheers David