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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-926004ac1b8sm1375302685a.36.2026.06.27.01.23.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 27 Jun 2026 01:23:56 -0700 (PDT) Date: Sat, 27 Jun 2026 04:23:52 -0400 From: Gregory Price To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, osalvador@suse.de, hannes@cmpxchg.org, mgorman@techsingularity.net, stable@vger.kernel.org Subject: Re: [PATCH] mm/vmstat: flush per-cpu node stats when a node goes offline Message-ID: References: <20260627073107.523499-1-gourry@gourry.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260627073107.523499-1-gourry@gourry.net> X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: A74C2C0002 X-Rspam-User: X-Stat-Signature: 83b4g3forowzttzd5tisfhxpj1m8ythz X-HE-Tag: 1782548638-215008 X-HE-Meta: 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 FzfKpljP d6HhWK1wfEW4wCvK8cpdjSBtTh9RPY5NiqL2jbMYAJ4svv8E91OYMiXvJXAho0VQ/MC4bqvLXgm0aGRtkpDmIK4sM+aQ1aoS29WQeUka6dW0MUWZTcQm8SgW9GlRus1mh9i/12/n3NeuBy5bx8vNnp2ataBLupONx5pSvXxKIEdfzPr13j9siPlOjeyqEeF4rOvgiNvRrlmjkw8EaNIXHN5CO7NeKWfUzpyJ+kdMolU+AKet1vmRb00zF2cGL1GuBqvGZ3TcUuVFPzS+PCfY3x2BZQuNAYFOOmufjP/pb/loNq9dFNMYyXnUXBVr+CAzqUfaLRDqhd5wXR7A= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Jun 27, 2026 at 03:31:07AM -0400, Gregory Price wrote: > > /* > * all memory/cpu of this node are removed, we can offline this > - * node now. > + * node now. Fold any pending per-cpu vmstat diffs into the global > + * counters first: once the node leaves the online set the periodic > + * fold skips it, orphaning the residual on a later online. > */ > + sync_vm_stats(); Sashiko points out this can deadlock on concurrent cpu hotplug, which after a quick look seems accurate. Has also made me realize the sync code is also racy with cpu hotplug as well as it iterates per-online-cpu. There are probably more races like this out there. Will need to give this a little more thought. > node_set_offline(nid); > unregister_node(nid); > }