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b=L42OIJw3fcppNGCJh7ojQVhFL4XvQRULZwFoEqHeP02rdBj9lBWmb8RNPaN2zNKBB ojz7Xjf3SXcFG+cKKsX/uZnnLfafDZTUe1aTqvde78thvl1JFj0UjviyHDkrbqsuBl Vgi6plUGKA/rulEES/v0MOtUPWWZ704idsk7pExM= Date: Mon, 9 Jun 2025 16:44:10 -0700 From: Andrew Morton To: Shakeel Butt Cc: Tejun Heo , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Vlastimil Babka , Alexei Starovoitov , Sebastian Andrzej Siewior , Michal =?ISO-8859-1?Q?Koutn=FD?= , Harry Yoo , Yosry Ahmed , bpf@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: Re: [PATCH 0/3] cgroup: nmi safe css_rstat_updated Message-Id: <20250609164410.568fd70e6a1deb6556e25af7@linux-foundation.org> In-Reply-To: <20250609225611.3967338-1-shakeel.butt@linux.dev> References: <20250609225611.3967338-1-shakeel.butt@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: s7gojj5rfw994eje9bti4udqw1w8bit5 X-Rspamd-Queue-Id: 331D440002 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1749512653-611491 X-HE-Meta: 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 m9S8C4sw Dd1TRCAdHv5bbgS1QL1x3xap3SPzQ2nC6uihGNJEUwjD+1exSvewtxqiY9cx2/sKIJXQpJrwozAUJ9Js9na9jNWQVDcdmQid38zNQhFhsn0zCNEZfD5xzvT5fyqFAtTCHc1XFYnMPumxYJkcS+/2GpIgxLleDIFH6zNCKrJZxLKPpEHJhpZDsbTu2sD+F5nulkPCTeYLztoN8k/QVMnl5IJOs8KZP0TwrD4gzM9UP8mhX/GjcLr2k3qgEs0l9RwFKuLbUK0rBH2+sD+YzJTFQE9cBaGzJEFvfnceBPbrL3IMWC6w= 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, 9 Jun 2025 15:56:08 -0700 Shakeel Butt wrote: > BPF programs can run in nmi context and may trigger memcg charged memory > allocation in such context. Recently linux added support to nmi safe > page allocation along with memcg charging of such allocations. However > the kmalloc/slab support and corresponding memcg charging is still > lacking, > > To provide nmi safe support for memcg charging for kmalloc/slab > allocations, we need nmi safe memcg stats and for that we need nmi safe > css_rstat_updated() which adds the given cgroup state whose stats are > updated into the per-cpu per-ss update tree. This series took the aim to > make css_rstat_updated() nmi safe. > > This series made css_rstat_updated by using per-cpu lockless lists whose > node in embedded in individual struct cgroup_subsys_state and the > per-cpu head is placed in struct cgroup_subsys. For rstat users without > cgroup_subsys, a global per-cpu lockless list head is created. The main > challenge to use lockless in this scenario was the potential multiple > inserters using the same lockless node of a cgroup_subsys_state which is > different from traditional users of lockless lists. > > The multiple inserters using potentially same lockless node was resolved > by making one of them succeed on reset the lockless node and the winner > gets to insert the lockless node in the corresponding lockless list. And what happens with the losers?