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[109.81.89.155]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-479310a6db3sm269869355e9.1.2025.12.08.10.15.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Dec 2025 10:15:25 -0800 (PST) Date: Mon, 8 Dec 2025 19:15:24 +0100 From: Michal Hocko To: Aboorva Devarajan Cc: Andrew Morton , gourry@gourry.net, david@kernel.org, vbabka@suse.cz, surenb@google.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/page_alloc: make percpu_pagelist_high_fraction reads lock-free Message-ID: References: <20251201060009.1420792-1-aboorvad@linux.ibm.com> <20251201094112.07eb1e588b6da2ee70c4641d@linux-foundation.org> 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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon 08-12-25 23:00:46, Aboorva Devarajan wrote: > On Mon, 2025-12-01 at 09:41 -0800, Andrew Morton wrote: > > On Mon,  1 Dec 2025 11:30:09 +0530 Aboorva Devarajan wrote: [...] > [83315.383433] page: refcount:2 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x4dc68 > [83315.383442] flags: 0x23ffffe00000000(node=2|zone=0|lastcpupid=0x1fffff) > [83315.383448] page_type: f5(slab) > [83315.383454] raw: 023ffffe00000000 c0000028e001fa00 5deadbeef0000100 5deadbeef0000122 > [83315.383462] raw: 0000000000000000 0000000001e101e1 00000002f5000000 0000000000000000 > [83315.383470] page dumped because: isolation failed > ... > ... > ... > > > Given the following statement in the documentation, should this behavior be considered > expected? > > >From Documentation/admin-guide/mm/memory-hotplug.rst: > "Further, memory offlining might retry for a long time (or even forever), until > aborted by the user." This is in line with trying to offline memory blocks containing the kernel memory as seen above. Retrying for ever on movable zones is a different issue as discussed in other reply. > There's also a TODO in the code that confirms this issue: > > mm/memory_hotplug.c > /* > * TODO: fatal migration failures should bail > * out > */ > do_migrate_range(pfn, end_pfn); > > > A possible improvement would be to add a retry limit or timeout for pages that repeatedly > fail isolation, returning -EBUSY after N attempts instead of looping indefinitely for > umovable pages. This would make the behavior more predictable. I disagree. It is trivial to implement timeout retry in the userspace. Any retry attempts limit behavior will be much less predictable. It could have been a matter of timing that an operation succeeds. We've had exactly that kind of behavior before. -- Michal Hocko SUSE Labs