netdev - Re: [PATCH v3] memcg: expose socket memory pressure in a cgroup

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Message-ID: <01ab2653-dbff-4a3f-ac91-f3f21a06dd2e@cdn77.com>
Date: Wed, 23 Jul 2025 10:41:30 +0200
From: Daniel Sedlak <daniel.sedlak@...77.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>,
 Kuniyuki Iwashima <kuniyu@...gle.com>
Cc: Michal Koutný <mkoutny@...e.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>, Roman Gushchin <roman.gushchin@...ux.dev>,
 Muchun Song <muchun.song@...ux.dev>, cgroups@...r.kernel.org,
 Matyas Hurtik <matyas.hurtik@...77.com>
Subject: Re: [PATCH v3] memcg: expose socket memory pressure in a cgroup

On 7/22/25 9:05 PM, Shakeel Butt wrote:
> On Tue, Jul 22, 2025 at 11:27:39AM -0700, Kuniyuki Iwashima wrote:
>> On Tue, Jul 22, 2025 at 10:50 AM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
>>>
>>> On Tue, Jul 22, 2025 at 10:57:31AM +0200, Michal Koutný wrote:
>>>> Hello Daniel.
>>>>
>>>> On Tue, Jul 22, 2025 at 09:11:46AM +0200, Daniel Sedlak <daniel.sedlak@...77.com> wrote:
>>>>>    /sys/fs/cgroup/**/<cgroup name>/memory.net.socket_pressure
>>>>>
>>>>> The output value is an integer matching the internal semantics of the
>>>>> struct mem_cgroup for socket_pressure. It is a periodic re-arm clock,
>>>>> representing the end of the said socket memory pressure, and once the
>>>>> clock is re-armed it is set to jiffies + HZ.
>>>>
>>>> I don't find it ideal to expose this value in its raw form that is
>>>> rather an implementation detail.
>>>>
>>>> IIUC, the information is possibly valid only during one jiffy interval.
>>>> How would be the userspace consuming this?
>>>>
>>>> I'd consider exposing this as a cummulative counter in memory.stat for
>>>> simplicity (or possibly cummulative time spent in the pressure
>>>> condition).
>>>>
>>>> Shakeel, how useful is this vmpressure per-cgroup tracking nowadays? I
>>>> thought it's kind of legacy.
>>>
>>>
>>> Yes vmpressure is legacy and we should not expose raw underlying number
>>> to the userspace. How about just 0 or 1 and use
>>> mem_cgroup_under_socket_pressure() underlying? In future if we change
>>> the underlying implementation, the output of this interface should be
>>> consistent.
>>
>> But this is available only for 1 second, and it will not be useful
>> except for live debugging ?
> 
> 1 second is the current implementation and it can be more if the memcg
> remains in memory pressure.

In our production environment, when this so-called pressure happens, it 
typically stays under pressure for a few hours straight. So, in our 
scenario, even a 1 or 0 would be helpful since it does not oscillate.