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

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Message-ID: <87a51rapi7.fsf@linux.dev>
Date: Wed, 15 Oct 2025 13:17:36 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Kuniyuki Iwashima <kuniyu@...gle.com>
Cc: Shakeel Butt <shakeel.butt@...ux.dev>,  Daniel Sedlak
 <daniel.sedlak@...77.com>,  "David S. Miller" <davem@...emloft.net>,  Eric
 Dumazet <edumazet@...gle.com>,  Jakub Kicinski <kuba@...nel.org>,  Paolo
 Abeni <pabeni@...hat.com>,  Simon Horman <horms@...nel.org>,  Jonathan
 Corbet <corbet@....net>,  Neal Cardwell <ncardwell@...gle.com>,  David
 Ahern <dsahern@...nel.org>,  Andrew Morton <akpm@...ux-foundation.org>,
  Yosry Ahmed <yosry.ahmed@...ux.dev>,  linux-mm@...ck.org,
  netdev@...r.kernel.org,  Johannes Weiner <hannes@...xchg.org>,  Michal
 Hocko <mhocko@...nel.org>,  Muchun Song <muchun.song@...ux.dev>,
  cgroups@...r.kernel.org,  Tejun Heo <tj@...nel.org>,  Michal Koutný
 <mkoutny@...e.com>,  Matyas Hurtik <matyas.hurtik@...77.com>
Subject: Re: [PATCH v5] memcg: expose socket memory pressure in a cgroup

Kuniyuki Iwashima <kuniyu@...gle.com> writes:

> On Wed, Oct 15, 2025 at 11:39 AM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
>>
>> On Wed, Oct 15, 2025 at 11:21:17AM -0700, Kuniyuki Iwashima wrote:
>> > On Tue, Oct 14, 2025 at 1:33 PM Shakeel Butt <shakeel.butt@...ux.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.
>> >
>>
>> 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