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

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Message-ID: <CANn89iJYv-ei-0yKzveLF7teyNpMUwTCf8YmOUzxZcyhowsTUQ@mail.gmail.com>
Date: Fri, 10 Oct 2025 07:23:47 -0700
From: Eric Dumazet <edumazet@...gle.com>
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>, 
	"David S. Miller" <davem@...emloft.net>, 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>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Kuniyuki Iwashima <kuni1840@...il.com>, bpf@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next/net 2/6] net: Allow opt-out from global protocol
 memory accounting.

On Mon, Oct 6, 2025 at 5:11 PM Kuniyuki Iwashima <kuniyu@...gle.com> 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.
>
> Sometimes, system processes do not want that limitation.  For a similar
> purpose, there is SO_RESERVE_MEM for sockets under memcg.
>
> Also, by opting out of the per-protocol accounting, sockets under memcg
> can avoid paying costs for two orthogonal memory accounting mechanisms.
> A microbenchmark result is in the subsequent bpf patch.
>
> Let's allow opt-out from the per-protocol memory accounting if
> sk->sk_bypass_prot_mem is true.
>
> sk->sk_bypass_prot_mem and sk->sk_prot are placed in the same cache
> line, and sk_has_account() always fetches sk->sk_prot before accessing
> sk->sk_bypass_prot_mem, so there is no extra cache miss for this patch.
>
> The following patches will set sk->sk_bypass_prot_mem to true, and
> then, the per-protocol memory accounting will be skipped.
>
> Note that this does NOT disable memcg, but rather the per-protocol one.
>
> Another option not to use the hole in struct sock_common is create
> sk_prot variants like tcp_prot_bypass, but this would complicate
> SOCKMAP logic, tcp_bpf_prots etc.
>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>