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From:   Eric Dumazet <edumazet@google.com>
Date:   Fri, 9 Jun 2023 11:07:05 +0200
Message-ID: <CANn89i+Qqq5nV0oRLh_KEHRV6VmSbS5PsSvayVHBi52FbB=sKA@mail.gmail.com>
Subject: Re: [RFC PATCH net-next] sock: Propose socket.urgent for sockmem isolation
To:     Abel Wu <wuyun.abel@bytedance.com>
Cc:     Tejun Heo <tj@kernel.org>, Christian Warloe <cwarloe@google.com>,
        Wei Wang <weiwan@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <muchun.song@linux.dev>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Ahern <dsahern@kernel.org>,
        Yosry Ahmed <yosryahmed@google.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Yu Zhao <yuzhao@google.com>,
        Vasily Averin <vasily.averin@linux.dev>,
        Kuniyuki Iwashima <kuniyu@amazon.com>,
        Martin KaFai Lau <martin.lau@kernel.org>,
        Xin Long <lucien.xin@gmail.com>,
        Jason Xing <kernelxing@tencent.com>,
        Michal Hocko <mhocko@suse.com>,
        Alexei Starovoitov <ast@kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@vger.kernel.org>,
        "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" 
        <cgroups@vger.kernel.org>,
        "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" 
        <linux-mm@kvack.org>
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On Fri, Jun 9, 2023 at 10:28=E2=80=AFAM Abel Wu <wuyun.abel@bytedance.com> =
wrote:
>
> This is just a PoC patch intended to resume the discussion about
> tcpmem isolation opened by Google in LPC'22 [1].
>
> We are facing the same problem that the global shared threshold can
> cause isolation issues. Low priority jobs can hog TCP memory and
> adversely impact higher priority jobs. What's worse is that these
> low priority jobs usually have smaller cpu weights leading to poor
> ability to consume rx data.
>
> To tackle this problem, an interface for non-root cgroup memory
> controller named 'socket.urgent' is proposed. It determines whether
> the sockets of this cgroup and its descendants can escape from the
> constrains or not under global socket memory pressure.
>
> The 'urgent' semantics will not take effect under memcg pressure in
> order to protect against worse memstalls, thus will be the same as
> before without this patch.
>
> This proposal doesn't remove protocal's threshold as we found it
> useful in restraining memory defragment. As aforementioned the low
> priority jobs can hog lots of memory, which is unreclaimable and
> unmovable, for some time due to small cpu weight.
>
> So in practice we allow high priority jobs with net-memcg accounting
> enabled to escape the global constrains if the net-memcg itselt is
> not under pressure. While for lower priority jobs, the budget will
> be tightened as the memory usage of 'urgent' jobs increases. In this
> way we can finally achieve:
>
>   - Important jobs won't be priority inversed by the background
>     jobs in terms of socket memory pressure/limit.
>
>   - Global constrains are still effective, but only on non-urgent
>     jobs, useful for admins on policy decision on defrag.
>
> Comments/Ideas are welcomed, thanks!
>

This seems to go in a complete opposite direction than memcg promises.

Can we fix memcg, so that :

Each group can use the memory it was provisioned (this includes TCP buffers=
)

Global tcp_memory can disappear (set tcp_mem to infinity)