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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 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 X-Rspamd-Queue-Id: BB2FE180003 X-Stat-Signature: 8jzpqp7q84u3e9ey6mfbj5isb6icun3z X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1767721939-246618 X-HE-Meta: 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 rt4VwY3s xbihJ 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 1/6/26 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