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[109.81.93.164]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47d7f661a03sm117662475e9.13.2026.01.07.09.17.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Jan 2026 09:17:31 -0800 (PST) Date: Wed, 7 Jan 2026 18:17:30 +0100 From: Michal Hocko To: Hannes Reinecke Cc: Gregory Price , 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 Subject: Re: [RFC PATCH] memory,memory_hotplug: allow restricting memory blocks to zone movable Message-ID: References: <20260105203611.4079743-1-gourry@gourry.net> <88dbe97c-3510-4ce7-ae85-067243a152bd@suse.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <88dbe97c-3510-4ce7-ae85-067243a152bd@suse.de> On Wed 07-01-26 13:47:41, Hannes Reinecke wrote: > 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. > It's not a policy per-se, but rather a udev rule (which one could > argue _is_ a policy, mind). There is a rather long-running SLES bug > around this if you are interested... I am aware of udev rules which automatically online memory that is hot added. But I am not aware of any rules to re-online memory that has been offlined. The former makes some sense while the latter makes very little sense to me. -- Michal Hocko SUSE Labs