From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A69EF38F24D; Thu, 19 Mar 2026 19:35:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773948949; cv=none; b=uS0tODDweeGaX1zj2vzMBSYV+KjZhgW+78J2KRWCK43fjR1uhsKMPM2FgLKVncqQ9f5dSswrjNF8WpLvNIo7xNiJ6KuDsKWQp18qt/qu0u7SWiffbJw50sjgFzkd2edR5oL4UMR57JIiLnoI17LA3JMaOBIZcPx9tqe041gIuHU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773948949; c=relaxed/simple; bh=GkPy7bpVDPzleX/dLk9OzmmYAqxzP1zWvyUhMm09gVA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dnDY7jmIZ27GFR8zfyzQzOvwaxCxQuUnKmZz64PL+I0Ewwunt9sWF7HB3NmZEYUZGFr0BrFgJiVE5k6ulYT9vZn+Bb8rar+K38GM/ZqY6GyvOl0/X+G7JB2scTt7FiUPrNlBibpg323WaST9aigV15mOslv1mXsC0F+sL3MDTho= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gpecay1/; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="gpecay1/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6001CC19424; Thu, 19 Mar 2026 19:35:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773948949; bh=GkPy7bpVDPzleX/dLk9OzmmYAqxzP1zWvyUhMm09gVA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=gpecay1/Nd1SFqKjJCFUwIJ/x2+UjLV+zrxL8yQ1TTQ6PvFqcJml+CiO81Gh5hpbD GQSdOCTFhWiw0DgD9kHeppcRmi38+a+U3fH/3WFhPZ6AT4kIgK5VDkTcI0JspLnF7Z 1I8Lpr9I2gF+Hu5L4UKJBP9yvncTNnDeEZmZ2ji4N8xX3bGNPVok4bR9XjEX6mOTmL EdD3euegiw1Wm0FPxZgNjcmUYl8ekEi4RASqNtRzIUCVBFiI8xdTbBahXQV/0ZYyq0 maE9pRilS+m/Eq1YQh1PQUk/oggDugIQZeLzBntDlZSVzwj1F4HQW+w92GpwG/ZQFc 8KrF4TPrQb74g== Message-ID: <96a0e49e-4b35-4e6c-a3f2-70891213db18@kernel.org> Date: Thu, 19 Mar 2026 20:35:44 +0100 Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: cxl/region.c improvements and DAX/Hotplug plumbing To: Gregory Price Cc: linux-cxl@vger.kernel.org, dan.j.williams@intel.com, dave.jiang@intel.com, jonathan.cameron@huawei.com, alison.schofield@intel.com, ira.weiny@intel.com, dave@stgolabs.net, linux-kernel@vger.kernel.org, kernel-team@meta.com, vishal.l.verma@intel.com, benjamin.cheatham@amd.com, David Rientjes References: <4d66eac3-1a2b-4d9d-8a9a-529a19758439@kernel.org> <217b154d-e4d1-4824-b2e3-fea82bc44402@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/19/26 16:14, Gregory Price wrote: > On Wed, Mar 18, 2026 at 09:53:05AM +0100, David Hildenbrand (Arm) wrote: >>> and would change the sysfs pattern to >>> echo regionN > cxl/decoder0.0/create_ram_region >>> echo regionN > cxl/drivers/sysram_region/bind >>> echo online_movable > cxl/devices/dax_regionN/hotplug >>> echo dax_regionN > cxl/drivers/dax_region/bind >>> >>> and gives the user a chance to configure a policy before the region >>> is pumped all the way through to the endpoint dax driver. >> >> Would that still be backwards-compatible? >> > > I've since squared this away with the CXL groups, the answer is a > different probe path and leaving the auto-probe logic alone. > > I still need to re-submit the /hotplug extensions here as an improvement > because its useful - but i've cleaned it up considerably to avoid the > cross-subsystem nonsense. > >>> >>> For most use-cases yes. For something like FAMFS (distributed shared >>> memory), one system onlining a block as kmem could be potentially >>> destructive to an entirely separate physical server. >> >> Right. But shouldn't we fail this already at the add_memory() stage? >> Sounds like during onlining is a bit too late. Conceptually, the hotplug >> as sysram was already wrong for famfs, or am I wrong? >> > > Mostly this describes the baggage associated with auto-hotplug path for > all CXL memory, and the fact that we only have a global-scope auto MHP > tag. I've come around to better solutions to this problem. I'm curious :) > > Thanks for the read n_n Sorry again for the late reply. -- Cheers, David