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

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Date: Wed, 6 Mar 2024 18:28:09 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: "Lameter, Christopher" <cl@...amperecomputing.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 Wed, Mar 6, 2024 at 6:01 PM Lameter, Christopher
<cl@...amperecomputing.com> wrote:
>
> On Wed, 28 Feb 2024, Eric Dumazet wrote:
>
> >> __sk_mem_raise_allocated() drops to 0.4%.
> >
> > I suspect some kind of flow/cpu steering issues then.
> > Also maybe SO_RESERVE_MEM would be better for this workload.
>
> This is via loopback. So there is a flow steering issue in the IP
> stack?

Asymmetric allocations / freeing, things that will usually have a high
cost for payload copy anyway.

Maybe a hierarchical tracking would avoid false sharings if some
arches pay a high price to them.

- One per-cpu reserve.    (X MB)

- One per-memory-domain reserve.  (number_of_cpu_in_this_domain * X MB)

- A global reserve, with an uncertainty of number_of_cpus * X MB

Basically reworking lib/percpu_counter.c for better NUMA awareness.