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

[Shakeel Butt <shakeel.butt@linux.dev>]

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:


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