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

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Message-ID: <13b5aeb6-ee0a-4b5b-a33a-e1d1d6f7f60e@cdn77.com>
Date: Thu, 9 Oct 2025 16:44:04 +0200
From: Daniel Sedlak <daniel.sedlak@...77.com>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: "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>,
 Kuniyuki Iwashima <kuniyu@...gle.com>, David Ahern <dsahern@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Shakeel Butt <shakeel.butt@...ux.dev>, 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

Hi Roman,

On 10/8/25 8:58 PM, Roman Gushchin wrote:
>> This patch exposes a new file for each cgroup in sysfs which is a
>> read-only single value file showing how many microseconds this cgroup
>> contributed to throttling the throughput of network sockets. The file is
>> accessible in the following path.
>>
>>    /sys/fs/cgroup/**/<cgroup name>/memory.net.throttled_usec
> 
> Hi Daniel!
> 
> How this value is going to be used? In other words, do you need an
> exact number or something like memory.events::net_throttled would be
> enough for your case?

Just incrementing a counter each time the vmpressure() happens IMO 
provides bad semantics of what is actually happening, because it can 
hide important details, mainly the _time_ for how long the network 
traffic was slowed down.

For example, when memory.events::net_throttled=1000, it can mean that 
the network was slowed down for 1 second or 1000 seconds or something 
between, and the memory.net.throttled_usec proposed by this patch 
disambiguates it.

In addition, v1/v2 of this series started that way, then from v3 we 
rewrote it to calculate the duration instead, which proved to be better 
information for debugging, as it is easier to understand implications.

Thanks!
Daniel