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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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Stat-Signature: ye5mmnwg53h5f7yhapsi5rcbe5a697eg X-Rspamd-Queue-Id: F37DD4000E X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1765217727-969802 X-HE-Meta: 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 S805iQ+l JftoShOXqAdzSxQ82TcWKklAeh7YGJ/rs0r5ptK2oeX7uF3itS/j+Su16VVvXM6fznZHW/vsRphiuEfx7A+p5H4QLWqaCSI8H1IW8FRLl4ANbz2ZQxal8kPssH90WsmhT+7mV2RmH7MrPmojUtQ3GHE19607OYau4YvTx4nZsZetMV/33HK2/ShlLJbRWQ5UZY2ZjSsojegNp+o7qvL/PNVIgRbs7y0EKSodVkdJ7cmKDa3GIhAwg4+CarRIFXkPZoVjFSk2sIDqIqk/R6+VY+X6GPFFuISLCYX2FlStje+bqHtnnrefrvFvQK/tyZ/MokhQr9DAwu8Ci8ZciPNzlm4xQaDnxqkgR4sxujKWD5xQO01+bANLeq/RfhbCrYUG3Eiu10PxU4EHEbLklEbbwD/h7LQYJo0Krxx1eelE/dy3iQHG1yrqgNuF7XsGYPqqSZmBs 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 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