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

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Message-ID: <20240227171316.40fe9c35@kernel.org>
Date: Tue, 27 Feb 2024 17:13:16 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: "Lameter, Christopher" <cl@...amperecomputing.com>
Cc: Eric Dumazet <edumazet@...gle.com>, Adam Li
 <adamli@...amperecomputing.com>, corbet@....net, davem@...emloft.net,
 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 15:08:18 -0800 (PST) Lameter, Christopher wrote:
> > 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...

We have a lot of machines at Meta with more cores than gigabytes of
memory. Keying on amount of memory would make sense. Something like
max(1MB, sk_mem / cores / 8) comes to mind?

In fact it may be a better idea to have the sysctl control the divisor
(the 8 in my example above). I had issues in the past with people
"micro-optimizing" the absolute size, forgetting about it, moving
workload to a larger machine and then complaining TCP is choking :(