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

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Date: Tue, 27 Feb 2024 21:38:29 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Adam Li <adamli@...amperecomputing.com>
Cc: 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, 
	cl@...amperecomputing.com, shijie@...amperecomputing.com
Subject: Re: [PATCH] net: make SK_MEMORY_PCPU_RESERV tunable

On Mon, Feb 26, 2024 at 3:25 AM Adam Li <adamli@...amperecomputing.com> wrote:
>
> This patch adds /proc/sys/net/core/mem_pcpu_rsv sysctl file,
> to make SK_MEMORY_PCPU_RESERV tunable.
>
> Commit 3cd3399dd7a8 ("net: implement per-cpu reserves for
> memory_allocated") introduced per-cpu forward alloc cache:
>
> "Implement a per-cpu cache of +1/-1 MB, to reduce number
> of changes to sk->sk_prot->memory_allocated, which
> would otherwise be cause of false sharing."
>
> 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.

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