netdev - Re: [PATCH v1 net-next 12/13] net-memcg: Store memcg->socket_isolated in sk->sk

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Message-ID: <CANn89iJk3B57ytDOEL8YpQj5K-LacKS0v1ANgLi5+cZr5gqTyQ@mail.gmail.com>
Date: Tue, 22 Jul 2025 08:02:08 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Neal Cardwell <ncardwell@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 
	Willem de Bruijn <willemb@...gle.com>, Matthieu Baerts <matttbe@...nel.org>, 
	Mat Martineau <martineau@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Hocko <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Shakeel Butt <shakeel.butt@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, 
	Simon Horman <horms@...nel.org>, Geliang Tang <geliang@...nel.org>, 
	Muchun Song <muchun.song@...ux.dev>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org, 
	mptcp@...ts.linux.dev, cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 net-next 12/13] net-memcg: Store memcg->socket_isolated
 in sk->sk_memcg.

On Mon, Jul 21, 2025 at 1:36 PM Kuniyuki Iwashima <kuniyu@...gle.com> wrote:
>
> memcg->socket_isolated can change at any time, so we must
> snapshot the value for each socket to ensure consistency.
>
> Given sk->sk_memcg can be accessed in the fast path, it would
> be preferable to place the flag field in the same cache line
> as sk->sk_memcg.
>
> However, struct sock does not have such a 1-byte hole.
>
> Let's store the flag in the lowest bit of sk->sk_memcg and
> add a helper to check the bit.
>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>

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