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[109.81.93.164]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-432bd0e175csm6163158f8f.14.2026.01.06.11.49.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Jan 2026 11:49:17 -0800 (PST) Date: Tue, 6 Jan 2026 20:49:16 +0100 From: Michal Hocko To: Gregory Price Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, david@redhat.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 Subject: Re: [RFC PATCH] memory,memory_hotplug: allow restricting memory blocks to zone movable Message-ID: References: <20260105203611.4079743-1-gourry@gourry.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 1D183120011 X-Stat-Signature: histi7fqzrx3zynsaktfhwdxe8w5a589 X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1767728958-161504 X-HE-Meta: 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 tJAS1obv PA7AmZUi6DrfIa1kTgSQHx5Wd1wazI8IGtWG/loqkfofUURpjgnSvB/soQES8DaqMd4fPczV+dVoDnsmeS6wWnWMJ70PZYE99Kzad89OAh23CYS1Y4MhHal18LwoWXRxE1tUixy7/BMZ7ei14tWm1aWWvtj7AGrbLRd4x7iSu/fDpE00LjMkNPtS81YnnNtptCyWhKIxPo/xeqfWCRTRRrt0hcwPOIbBYHBQDqUq5wng3WQWyuD/5YoGVcBtvJepNStcMknAwVAaLErlorTWJRGEqHm8yJxowiEniZRS8I9nfw90IM9UFg8h51eGH0QRFpf5d7c7nEL2nqp/WYHjmf5qWd6YPQ8+Eo30w5FT5yuhnsdl/V/UypL8xBNsQcp9eeKE242CmtdNCPFQ+QeigBEwg9A== 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 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. -- Michal Hocko SUSE Labs