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Tue, 29 Jul 2025 07:22:48 -0700 (PDT) Date: Tue, 29 Jul 2025 10:22:46 -0400 From: Johannes Weiner To: Kuniyuki Iwashima Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Neal Cardwell , Paolo Abeni , Willem de Bruijn , Matthieu Baerts , Mat Martineau , Michal Hocko , Roman Gushchin , Shakeel Butt , Andrew Morton , Simon Horman , Geliang Tang , Muchun Song , Kuniyuki Iwashima , netdev@vger.kernel.org, mptcp@lists.linux.dev, cgroups@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v1 net-next 13/13] net-memcg: Allow decoupling memcg from global protocol memory accounting. Message-ID: <20250729142246.GF54289@cmpxchg.org> References: <20250721203624.3807041-1-kuniyu@google.com> <20250721203624.3807041-14-kuniyu@google.com> <20250728160737.GE54289@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: 4588C4000C X-Rspam-User: X-Rspamd-Server: rspam09 X-Stat-Signature: gmh7mpnkmukusomff51ee8xanothz8t3 X-HE-Tag: 1753798970-638907 X-HE-Meta: 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 pxHi3Emr 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 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, Jul 28, 2025 at 02:41:38PM -0700, Kuniyuki Iwashima wrote: > On Mon, Jul 28, 2025 at 9:07 AM Johannes Weiner wrote: > > > > On Mon, Jul 21, 2025 at 08:35:32PM +0000, Kuniyuki Iwashima wrote: > > > Some protocols (e.g., TCP, UDP) implement memory accounting for socket > > > buffers and charge memory to per-protocol global counters pointed to by > > > sk->sk_proto->memory_allocated. > > > > > > When running under a non-root cgroup, this memory is also charged to the > > > memcg as sock in memory.stat. > > > > > > Even when memory usage is controlled by memcg, sockets using such protocols > > > are still subject to global limits (e.g., /proc/sys/net/ipv4/tcp_mem). > > > > > > This makes it difficult to accurately estimate and configure appropriate > > > global limits, especially in multi-tenant environments. > > > > > > If all workloads were guaranteed to be controlled under memcg, the issue > > > could be worked around by setting tcp_mem[0~2] to UINT_MAX. > > > > > > In reality, this assumption does not always hold, and a single workload > > > that opts out of memcg can consume memory up to the global limit, > > > becoming a noisy neighbour. > > > > Yes, an uncontrolled cgroup can consume all of a shared resource and > > thereby become a noisy neighbor. Why is network memory special? > > > > I assume you have some other mechanisms for curbing things like > > filesystem caches, anon memory, swap etc. of such otherwise > > uncontrolled groups, and this just happens to be your missing piece. > > I think that's the tcp_mem[] knob, limiting tcp mem globally for > the "uncontrolled" cgroup. But we can't use it because the > "controlled" cgroup is also limited by this knob. No, I was really asking what you do about other types of memory consumed by such uncontrolled cgroups. You can't have uncontrolled groups and complain about their resource consumption.