Kuniyuki Iwashima [off-list ref] writes:

On Wed, Oct 15, 2025 at 11:39 AM Shakeel Butt [off-list ref] wrote:

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On Wed, Oct 15, 2025 at 11:21:17AM -0700, Kuniyuki Iwashima wrote:

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On Tue, Oct 14, 2025 at 1:33 PM Shakeel Butt [off-list ref] wrote:

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On Mon, Oct 13, 2025 at 04:30:53PM +0200, Daniel Sedlak wrote:
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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.

I wanted to start simple and focus on one specific action but I am open
to other actins as well. Do we want a generic network throttled metric
or do we want different metric for different action? At the moment I
think for memcg, a single metric would be sufficient and then we can
have tracepoints for more fine grained debugging.

I agree that a single metric would be enough if it can signal
something bad is happening as a first step, then we can take
further action with tracepoint, bpftrace, whatever.

+1 to a single metric