netdev - Re: [PATCH v10 bpf-next/net 3/6] net-memcg: Introduce net.core.memcg

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Message-ID: <CAAVpQUA+6BQhCt01AgEnST3=K46jbeRpPvYMrk_Fu8OhtHrP7A@mail.gmail.com>
Date: Mon, 22 Sep 2025 18:26:33 -0700
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
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 3/6] net-memcg: Introduce
 net.core.memcg_exclusive sysctl.

On Mon, Sep 22, 2025 at 6:03 PM Kuniyuki Iwashima <kuniyu@...gle.com> wrote:
>
> On Mon, Sep 22, 2025 at 5:54 PM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> >
> > On Sat, Sep 20, 2025 at 12:07:17AM +0000, Kuniyuki Iwashima wrote:
> > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > index 814966309b0e..348e599c3fbc 100644
> > > --- a/net/core/sock.c
> > > +++ b/net/core/sock.c
> > > @@ -2519,6 +2519,7 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
> > >  #ifdef CONFIG_MEMCG
> > >       /* sk->sk_memcg will be populated at accept() time */
> > >       newsk->sk_memcg = NULL;
> > > +     mem_cgroup_sk_set_flags(newsk, mem_cgroup_sk_get_flags(sk));
> >
> > Why do you need to set the flag here? Will doing in __inet_accept only
> > be too late i.e. protocol accounting would have happened?

Oh no, this is because I used newsk in __inet_accept(), and
we can use sock->sk in __inet_accept() and remove the inheritance
in sk_clone_lock() like this,

flags = mem_cgroup_sk_get_flags(sock->sk);

but I think using newsk reduces one cache miss.  Also, we touch the
parent sk_memcg during sock_copy() in sk_clone_lock().