linux-kernel - Re: [RFC PATCH net-next] sock: Propose socket.urgent for sockmem isolation

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Message-ID: <42285da4-ea80-78ca-4c71-6562170614c8@bytedance.com>
Date:   Fri, 16 Jun 2023 15:27:24 +0800
From:   Abel Wu <wuyun.abel@...edance.com>
To:     Eric Dumazet <edumazet@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>
Cc:     Tejun Heo <tj@...nel.org>, Christian Warloe <cwarloe@...gle.com>,
        Wei Wang <weiwan@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Ahern <dsahern@...nel.org>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Yu Zhao <yuzhao@...gle.com>,
        Vasily Averin <vasily.averin@...ux.dev>,
        Kuniyuki Iwashima <kuniyu@...zon.com>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        Xin Long <lucien.xin@...il.com>,
        Jason Xing <kernelxing@...cent.com>,
        Michal Hocko <mhocko@...e.com>,
        Alexei Starovoitov <ast@...nel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" 
        <cgroups@...r.kernel.org>,
        "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" 
        <linux-mm@...ck.org>
Subject: Re: [RFC PATCH net-next] sock: Propose socket.urgent for sockmem
 isolation

Gentle ping :)

Any suggestions for memory over-committed scenario?

Thanks,
	Abel

On 6/13/23 2:46 PM, Abel Wu wrote:
> On 6/9/23 5:07 PM, Eric Dumazet wrote:
>> On Fri, Jun 9, 2023 at 10:28 AM Abel Wu <wuyun.abel@...edance.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)
> 
> Yes, but might not be easy once memory gets over-committed (which is
> common in modern data-centers). So as a tradeoff, we intend to put
> harder constraint on memory allocation for low priority jobs. Or else
> if every job can use its provisioned memory, than there will be more
> memstalls blocking random jobs which could be the important ones.
> Either way hurts performance, but the difference is whose performance
> gets hurt.
> 
> Memory protection (memory.{min,low}) helps the important jobs less
> affected by memstalls. But once low priority jobs use lots of kernel
> memory like sockmem, the protection might become much less efficient.
> 
>>
>> Global tcp_memory can disappear (set tcp_mem to infinity)