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Date: Wed, 17 Sep 2025 12:18:28 -0700
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Subject: Re: [PATCH v8 bpf-next/net 2/6] net-memcg: Allow decoupling memcg
 from global protocol memory accounting.
To: Kuniyuki Iwashima <kuniyu@google.com>,
 Shakeel Butt <shakeel.butt@linux.dev>, Johannes Weiner <hannes@cmpxchg.org>
Cc: Alexei Starovoitov <ast@kernel.org>, Andrii Nakryiko <andrii@kernel.org>,
 Daniel Borkmann <daniel@iogearbox.net>,
 John Fastabend <john.fastabend@gmail.com>,
 Stanislav Fomichev <sdf@fomichev.me>, Michal Hocko <mhocko@kernel.org>,
 Roman Gushchin <roman.gushchin@linux.dev>,
 "David S. Miller" <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>,
 Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
 Neal Cardwell <ncardwell@google.com>, Willem de Bruijn <willemb@google.com>,
 Mina Almasry <almasrymina@google.com>, Kuniyuki Iwashima
 <kuni1840@gmail.com>, bpf@vger.kernel.org, netdev@vger.kernel.org
References: <20250910192057.1045711-1-kuniyu@google.com>
 <20250910192057.1045711-3-kuniyu@google.com>
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From: Martin KaFai Lau <martin.lau@linux.dev>
In-Reply-To: <20250910192057.1045711-3-kuniyu@google.com>
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On 9/10/25 12:19 PM, 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.
> 
> If a socket has sk->sk_memcg, this memory is also charged to memcg as
> "sock" in memory.stat.
> 
> We do not need to pay costs for two orthogonal memory accounting
> mechanisms.  A microbenchmark result is in the subsequent bpf patch.
> 
> Let's decouple sockets under memcg from the global per-protocol memory
> accounting if mem_cgroup_sk_exclusive() returns true.
> 
> Note that this does NOT disable memcg, but rather the per-protocol one.

The bpf side changes look reasonable. I believe the commit message in v8 has 
clarified the reason and its behavior. memcg reviewers, please take a look.