netdev - Re: [PATCH net-next] tcp: account for memory pressure signaled by cgroup

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Message-ID: <4a8ce60d-fd28-4df9-b568-99964fed837c@cdn77.com>
Date: Tue, 8 Jul 2025 11:08:04 +0200
From: Daniel Sedlak <daniel.sedlak@...77.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>, Jonathan Corbet <corbet@....net>,
 Neal Cardwell <ncardwell@...gle.com>, Kuniyuki Iwashima <kuniyu@...gle.com>,
 David Ahern <dsahern@...nel.org>, Jiayuan Chen <jiayuan.chen@...ux.dev>,
 Christian Hopps <chopps@...n.net>, Sabrina Dubroca <sd@...asysnail.net>,
 netdev@...r.kernel.org, linux-doc@...r.kernel.org,
 Matyas Hurtik <matyas.hurtik@...77.com>
Subject: Re: [PATCH net-next] tcp: account for memory pressure signaled by
 cgroup

On 7/8/25 9:01 AM, Eric Dumazet wrote:
> On Mon, Jul 7, 2025 at 11:45 PM Daniel Sedlak <daniel.sedlak@...77.com> wrote:
>>
>> Hi Eric,
>> Thank you for your feedback.
>>
>> On 7/7/25 2:48 PM, Eric Dumazet wrote:
>>> On Mon, Jul 7, 2025 at 3:55 AM Daniel Sedlak <daniel.sedlak@...77.com> wrote:
>>>>
>>>> Currently, we have two memory pressure counters for TCP sockets [1],
>>>> which we manipulate only when the memory pressure is signalled through
>>>> the proto struct [2].
>>>>
>>>> However, the memory pressure can also be signaled through the cgroup
>>>> memory subsystem, which we do not reflect in the netstat counters.
>>>>
>>>> This patch adds a new counter to account for memory pressure signaled by
>>>> the memory cgroup.
>>>
>>> OK, but please amend the changelog to describe how to look at the
>>> per-cgroup information.
>>
>> Sure, I will explain it more in v2. I was not sure how much of a
>> "storytelling" is appropriate in the commit message.
>>
>>
>>> I am sure that having some details on how to find the faulty cgroup
>>> would also help.
>>
>> Right now, we have a rather fragile bpftrace script for that, but we
>> have a WIP patch for memory management, which will expose which cgroup
>> is having "difficulties", but that is still ongoing work.
>>
>> Or do you have any suggestions on how we can incorporate this
>> information about "this particular cgroup is under pressure" into the
>> net subsystem? Maybe a log line?
> 
> Perhaps an additional trace point ?

Sounds good to me, we will incorporate that and send v2.
> 
> Ideally we could trace the cgroup path, or at least the pid.

Will try to do both, we will see.

Thanks!
Daniel