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 5E46E3612E8 for ; Wed, 7 Jan 2026 15:09:42 +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=1767798582; cv=none; b=PjTDtxiePloKUw+P9+Jw10kbtzmUFWsbS9EPOeIgNQmQvPhh/nreSjE3Mvm3qTIG5BjESAWD/1bdSu9AyyVoyqdOc98vqaNgisauNNVL0V8WI/5AKVfCmurD+FjvMjK58MzVDSBEVQ1VBdpl3qfa3h7JQeDasofJN1vSsbZr4ko= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767798582; c=relaxed/simple; bh=wTafYNIje0IAQr4XFgtXKuH0/8MFPDAFFvntDIO066E=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SlcNO71kZ3QZssk0tpJB8NZvQuEQRr8wxVL6bTHIfMkVKHY6d3SvWy85kcJK9XHu6dQ9aW6fWDwwoKmZEBZg4tNKf2gQeNlYBtzk77pj+uH/IF7TBryUoLHJI2w4hTw0YpjgudrifNoF6Pw7iDx04KmTKYo1sdefnhuhsYMCpEg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=l7EkdduQ; 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="l7EkdduQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C94BC4CEF7; Wed, 7 Jan 2026 15:09:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767798581; bh=wTafYNIje0IAQr4XFgtXKuH0/8MFPDAFFvntDIO066E=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=l7EkdduQblfvPk5R/a8xHq9uqL35tj1I53o25XjzvCvGGWEMWRg2QDr7y2zE1gWQi s7LrncVkGlrC2XjxgeGpgbqzr8nsNTaJmKolKazosuhj86VX5opdQfHau2Wsj+rZ++ 2w2iGkyqmT6L9CaoUCsJpWK8mM2MQTYkyR70wXXOdpgBlaE3Xr4uTrX62ZKJQiA4EB ZgqCHo4komeB7klWJ4MfJ1seSq2zOZ+/YNbFgyi0Gw2lT6sUhB0AXSjYj1YrQCH5cb IeTCJi02fBquxDFi5xtW8d0wvtSgIeB9d/H/teb+FlQbmR/8hWglQGQjIYrKd7LHn8 TMvQUWQQ8uYcg== Message-ID: <39533aa8-ca78-41a8-b005-9202ce53e3ae@kernel.org> Date: Wed, 7 Jan 2026 16:09:34 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] memory,memory_hotplug: allow restricting memory blocks to zone movable To: Michal Hocko , Gregory Price Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, osalvador@suse.de, gregkh@linuxfoundation.org, rafael@kernel.org, dakr@kernel.org, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, hare@suse.de References: <20260105203611.4079743-1-gourry@gourry.net> 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 On 1/6/26 20:49, Michal Hocko wrote: > On Tue 06-01-26 11:53:30, Gregory Price wrote: >> On Tue, Jan 06, 2026 at 04:05:48PM +0100, Michal Hocko wrote: >>> On Mon 05-01-26 15:36:11, Gregory Price wrote: >>>> It was reported (LPC 2025) that userland services which monitor memory >>>> blocks can cause hot-unplug to fail permanently. >>>> >>>> This can occur when drivers attempt to hot-remove memory in two phases >>>> (offline, remove), while a userland service detects the memory offline >>>> and re-onlines the memory into a zone which may prevent removal. >>> >>> Are there more details about this? >> >> The details are with Hannes, I was just recapping what was described in >> his devmem talk at LPC ("To online or not online"). > > I know of policies to online newly added memory blocks but I am not > aware of policies to re-online something that has been made offline. > >>> That being said, rather than movable_only, should we have a mask of >>> online types supported for the mem block? >>> >> >> I briefly considered this. I went with this for RFC-v1 since it's >> fairly simple and because movable is really the only zone with hotplug >> guarantees (any other zone makes no hotplug guarantees). >> >> It's also significantly more complex of a change for questionable value, >> but if people see this as the way to go i'll happily pivot to that. > > Sure, I wouldn't push for more complexity just for the sake of a > theoretical extensibility. And I have to admit I have't tried to a quick > PoC to see how complex this could grow. I was hoping this could get into > a simple mask for online types with default MMOP_ONLINE_KERNEL|MMOP_ONLINE_MOVABLE > and special cases just choosing one of the two and zone_for_pfn_range > checking for the compatibility with the requested online type. But I do > appreciate there might be some obstacles on the way to achieve that. If we want to go down that path of failing onlining, we could likely do without any core-MM changes: dax can simply register a memory notifier and fail MEM_GOING_ONLINE of its memory with -EINVAL when it sees !ZONE_MOVABLE. That works, because online_pages() does the move_pfn_range_to_zone() before calling MEM_GOING_ONLINE. -- Cheers David