linux-kernel - Re: [PATCH] net: make SK_MEMORY_PCPU

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Message-ID: <bc168824-25dd-7541-1a34-38b1a3c00489@os.amperecomputing.com>
Date: Tue, 27 Feb 2024 15:08:18 -0800 (PST)
From: "Lameter, Christopher" <cl@...amperecomputing.com>
To: Eric Dumazet <edumazet@...gle.com>
cc: Adam Li <adamli@...amperecomputing.com>, corbet@....net, 
    davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, 
    willemb@...gle.com, yangtiezhu@...ngson.cn, atenart@...nel.org, 
    kuniyu@...zon.com, wuyun.abel@...edance.com, leitao@...ian.org, 
    alexander@...alicyn.com, dhowells@...hat.com, paulmck@...nel.org, 
    joel.granados@...il.com, urezki@...il.com, joel@...lfernandes.org, 
    linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
    netdev@...r.kernel.org, patches@...erecomputing.com, 
    shijie@...amperecomputing.com
Subject: Re: [PATCH] net: make SK_MEMORY_PCPU_RESERV tunable

On Tue, 27 Feb 2024, Eric Dumazet wrote:

>> sk_prot->memory_allocated points to global atomic variable:
>> atomic_long_t tcp_memory_allocated ____cacheline_aligned_in_smp;
>>
>> If increasing the per-cpu cache size from 1MB to e.g. 16MB,
>> changes to sk->sk_prot->memory_allocated can be further reduced.
>> Performance may be improved on system with many cores.
>
> This looks good, do you have any performance numbers to share ?
>
> On a host with 384 threads, 384*16 ->  6 GB of memory.

Those things also come with corresponding memories of a couple of TB...

> With this kind of use, we might need a shrinker...

Yes. No point of keeping the buffers around if the core stops doing 
networking. But to be done at times when there is no contention please. 
Isnt there something like a timeout for skbs in the network stack already?