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 C5DC62FB630 for ; Tue, 6 Jan 2026 17:52:18 +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=1767721938; cv=none; b=SOwjY+H6oC7sTtOw2GYpCjKb0+NKRXaBNle2izqHPKtPWt1sWmH7i2Xp1uzvM8pP2AuXyJwRQ1C6SdXhaD1u+VUpa6Y3vSu0jJVYY6lIhKa0GeKSHUOPbQxBrVL3QIbgLTOImrkMFV4pYkm5bDhwwOzV/EzYRmwjgrscI7Brvgc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767721938; c=relaxed/simple; bh=p1c3WMeUaHTT26OVRketCaLs++7iT/cuCyQgsuGHZIg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Z0PD6sOcoXBCFmnNN/cEMuqo06xGZ5ISWd1/nUKCTZvgzYo9a9bjBwJapHjMeBeLYAf5X2+S5tzhRjT+RerkqUKQWVUP9rxZptgPysl+OTSjzvb8J7rFATRMa9d8Lx6oajJMeRYqh8J0n0B8FKzPbqWDZ3mXidZCGEq+PoaOiSA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IbPCy0It; 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="IbPCy0It" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 10D18C116C6; Tue, 6 Jan 2026 17:52:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767721938; bh=p1c3WMeUaHTT26OVRketCaLs++7iT/cuCyQgsuGHZIg=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=IbPCy0It3SRpYwFSDcRT1suC5krs1BsSmVkpDa3GSz4AoBiDOk2SLido9BDPE6+tw o6S//pbNCzHmzNhiVS/RMdb8z4SULvMlbDR1mGJoj/kVB5wXNZs+tkSUyvBpdbBHlQ 1bPAyPvVhYhXOUrv2KTmH3Ou9JkV6braCMg6E6K57RynXGfK/gMd8R8IsCxiTZKXxg SN7t8OUkY+V6xdFq9oaDSAdjyPVXnzGKH1idzHDZKZlasJMVjicRgGEt+EFUQ7L0JI bFDxF0YobYZx5ky34zeue8BR8W6NLU9M/sbiNSKnvcPHGtFMYmBzqOwZBobA6lz2Er 2p0emrh5DWvgw== Message-ID: <9575e042-39f4-4f01-80db-34aaaa9312e6@kernel.org> Date: Tue, 6 Jan 2026 18:52:11 +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: 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, mhocko@suse.com, hare@suse.de References: <20260105203611.4079743-1-gourry@gourry.net> <7f053290-6b9a-4d18-936e-0f28006c79c3@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 On 1/6/26 17:58, Gregory Price wrote: > On Tue, Jan 06, 2026 at 04:24:21PM +0100, David Hildenbrand (Red Hat) wrote: >>> +/* >>> + * Restrict hotplugged memory blocks to ZONE_MOVABLE only. >>> + * >>> + * During offlining of hotplugged memory which was originally onlined >>> + * as ZONE_MOVABLE, userland services may detect blocks going offline >>> + * and automatically re-online them into ZONE_NORMAL or lower. When >>> + * this happens it may become permanently incapable of being removed. >> >> If it's really only that, we could also look into simply making a re-online >> without a specific mode ("online") to use the previous mode. >> >> We could glue that to the "contig-zones" policy only, to not affect >> "auto-movable". >> >> That is, remember the zone to which it was previously onlined, and then >> simply re-online to that one. >> > > I know we do this in memory_hotplug.c to rollback to prior state. > > I did notice in... i think it was either memory.c or hotplug.c... that > we end up setting mem->online_type=MMOP_OFFLINE after comping an online > operation. That seemed confusing and maybe we can use that to store the > current state. > > I'm not against this idea, but it also makes the sysfs a little more > confusing (`echo online` now does different things based on prior > state). Right, but only for the contig-zones policy. But maybe you really want the default for such memory to be "movable" even when not onlined beforehand? So I am not sure if the description of the problem here is accurate. Isn't one problem also udev racing with ndctl? > I preferred just failing if the block wasn't compatible with > the zone (maybe making it more clear with a dmesg print?) The thing is that this block is compatible with the zone, no? In a system where you would never want to offline that memory, why should we stop someone from onlining it to a kernel zone? I'm sure someone with a weird use case will show up later that will complain about this. But the patch is missing details on who would actually set MHP_MOVABLE_ONLY. A user should be posted alongside the core change. > > Anyway, let me know what your preference is, happy to pivot however. Restricting memory to be movable-only to handle a user-space problem as described here sounds like the wrong approach to me. You really want the default of such memory to be "movable". Almost like an optimized "auto-movable" policy :) Or a new policy that will respect a provided default (MHP_DEFAULT_MOVABLE). -- Cheers David