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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 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 X-Rspam-User: X-Rspamd-Queue-Id: 18165A0007 X-Rspamd-Server: rspam10 X-Stat-Signature: 9ssk976fumghzx4tg38drfgu7arhejfp X-HE-Tag: 1767798582-186554 X-HE-Meta: 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 hnxRxwhK fV6VE5bHiRUFJi/aHTLb35Jig1NdQ/2Gl3o6DU5B2c2tweSG65WVWJ8ByFkTOYzoZdBKglDE/3kTVd4v6wFnbYSGPhn8ekIg/IKy8hgjFI+trXJvwCgY0WiX0c+Jdv2yxOHUZ3vErjHql2rGv8m69bGyMO/4mtcAfItDXZif/En+7bSxbrzMv/6v1VOvw469PRAi2oRi77e0Vumm3scp0se4B+MQggKJy2FPg3GBJazlIUSQm54VFYncktcDqXMojkldGqMQV1IKtpvxtBSgyMMNXpxQIjKzcWxxKzs1sLKUI4xq/3b87iimtYg== 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 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