netdev - Re: [PATCH v10 bpf-next/net 2/6] net-memcg: Allow decoupling memcg from global protocol memory accounting.

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Message-ID: <ddrg3ex7rbogxeacbegm3e7bewb2rmnxccw4jsyhdpdksz2qng@2xbs7jvhzzhk>
Date: Fri, 19 Sep 2025 22:25:26 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Kuniyuki Iwashima <kuniyu@...gle.com>
Cc: Alexei Starovoitov <ast@...nel.org>, 
	Andrii Nakryiko <andrii@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	Stanislav Fomichev <sdf@...ichev.me>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Hocko <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Neal Cardwell <ncardwell@...gle.com>, Willem de Bruijn <willemb@...gle.com>, 
	Mina Almasry <almasrymina@...gle.com>, Kuniyuki Iwashima <kuni1840@...il.com>, bpf@...r.kernel.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH v10 bpf-next/net 2/6] net-memcg: Allow decoupling memcg
 from global protocol memory accounting.

On Sat, Sep 20, 2025 at 12:07:16AM +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.
> 
> 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.
> 
> mem_cgroup_sk_exclusive() starts to return true in the following patches,
> and then, the per-protocol memory accounting will be skipped.
> 
> In __inet_accept(), we need to reclaim counts that are already charged
> for child sockets because we do not allocate sk->sk_memcg until accept().
> 
> trace_sock_exceed_buf_limit() will always show 0 as accounted for the
> memcg-exclusive sockets, but this can be obtained in memory.stat.
> 
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
> Nacked-by: Johannes Weiner <hannes@...xchg.org>

This looks good to me now, let's ask Johannes to take a look again and if
he still has any concerns.

Reviewed-by: Shakeel Butt <shakeel.butt@...ux.dev>