Re: [PATCH v5] memcg: expose socket memory pressure in a cgroup

[Kuniyuki Iwashima <kuniyu@google.com>]

On Tue, Oct 14, 2025 at 1:33 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
>
> On Mon, Oct 13, 2025 at 04:30:53PM +0200, Daniel Sedlak wrote:
> [...]
> > > > > > How about we track the actions taken by the callers of
> > > > > > mem_cgroup_sk_under_memory_pressure()? Basically if network stack
> > > > > > reduces the buffer size or whatever the other actions it may take when
> > > > > > mem_cgroup_sk_under_memory_pressure() returns, tracking those actions
> > > > > > is what I think is needed here, at least for the debugging use-case.
> >
> > I am not against it, but I feel that conveying those tracked actions (or how
> > to represent them) to the user will be much harder. Are there already
> > existing APIs to push this information to the user?
> >
>
> I discussed with Wei Wang and she suggested we should start tracking the
> calls to tcp_adjust_rcv_ssthresh() first. So, something like the
> following. I would like feedback frm networking folks as well:

I think we could simply put memcg_memory_event() in
mem_cgroup_sk_under_memory_pressure() when it returns
true.

Other than tcp_adjust_rcv_ssthresh(), if tcp_under_memory_pressure()
returns true, it indicates something bad will happen, failure to expand
rcvbuf and sndbuf, need to prune out-of-order queue more aggressively,
FIN deferred to a retransmitted packet.

Also, we could cover mptcp and sctp too.



>
>
> From 54bd2bf6681c1c694295646532f2a62a205ee41a Mon Sep 17 00:00:00 2001
> From: Shakeel Butt <shakeel.butt@linux.dev>
> Date: Tue, 14 Oct 2025 13:27:36 -0700
> Subject: [PATCH] memcg: track network throttling due to memcg memory pressure
>
> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
> ---
>  include/linux/memcontrol.h | 1 +
>  mm/memcontrol.c            | 2 ++
>  net/ipv4/tcp_input.c       | 5 ++++-
>  net/ipv4/tcp_output.c      | 8 ++++++--
>  4 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 873e510d6f8d..5fe254813123 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -52,6 +52,7 @@ enum memcg_memory_event {
>         MEMCG_SWAP_HIGH,
>         MEMCG_SWAP_MAX,
>         MEMCG_SWAP_FAIL,
> +       MEMCG_SOCK_THROTTLED,
>         MEMCG_NR_MEMORY_EVENTS,
>  };
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 4deda33625f4..9207bba34e2e 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4463,6 +4463,8 @@ static void __memory_events_show(struct seq_file *m, atomic_long_t *events)
>                    atomic_long_read(&events[MEMCG_OOM_KILL]));
>         seq_printf(m, "oom_group_kill %lu\n",
>                    atomic_long_read(&events[MEMCG_OOM_GROUP_KILL]));
> +       seq_printf(m, "sock_throttled %lu\n",
> +                  atomic_long_read(&events[MEMCG_SOCK_THROTTLED]));
>  }
>
>  static int memory_events_show(struct seq_file *m, void *v)
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 31ea5af49f2d..2206968fb505 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -713,6 +713,7 @@ static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb,
>                  * Adjust rcv_ssthresh according to reserved mem
>                  */
>                 tcp_adjust_rcv_ssthresh(sk);
> +               memcg_memory_event(sk->sk_memcg, MEMCG_SOCK_THROTTLED);
>         }
>  }
>
> @@ -5764,8 +5765,10 @@ static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb)
>
>         if (!tcp_can_ingest(sk, in_skb))
>                 tcp_clamp_window(sk);
> -       else if (tcp_under_memory_pressure(sk))
> +       else if (tcp_under_memory_pressure(sk)) {
>                 tcp_adjust_rcv_ssthresh(sk);
> +               memcg_memory_event(sk->sk_memcg, MEMCG_SOCK_THROTTLED);
> +       }
>
>         if (tcp_can_ingest(sk, in_skb))
>                 return 0;
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index bb3576ac0ad7..8fe8d973d7ac 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -3275,8 +3275,10 @@ u32 __tcp_select_window(struct sock *sk)
>         if (free_space < (full_space >> 1)) {
>                 icsk->icsk_ack.quick = 0;
>
> -               if (tcp_under_memory_pressure(sk))
> +               if (tcp_under_memory_pressure(sk)) {
>                         tcp_adjust_rcv_ssthresh(sk);
> +                       memcg_memory_event(sk->sk_memcg, MEMCG_SOCK_THROTTLED);
> +               }
>
>                 /* free_space might become our new window, make sure we don't
>                  * increase it due to wscale.
> @@ -3334,8 +3336,10 @@ u32 __tcp_select_window(struct sock *sk)
>         if (free_space < (full_space >> 1)) {
>                 icsk->icsk_ack.quick = 0;
>
> -               if (tcp_under_memory_pressure(sk))
> +               if (tcp_under_memory_pressure(sk)) {
>                         tcp_adjust_rcv_ssthresh(sk);
> +                       memcg_memory_event(sk->sk_memcg, MEMCG_SOCK_THROTTLED);
> +               }
>
>                 /* if free space is too low, return a zero window */
>                 if (free_space < (allowed_space >> 4) || free_space < mss ||
> --
> 2.47.3
>