netdev - Re: [PATCH net-next 1/2] net: Keep sk->sk_forward

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Date: Thu, 1 Jun 2023 05:21:51 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: "Zhang, Cathy" <cathy.zhang@...el.com>
Cc: Shakeel Butt <shakeelb@...gle.com>, "Sang, Oliver" <oliver.sang@...el.com>, 
	"Yin, Fengwei" <fengwei.yin@...el.com>, "Tang, Feng" <feng.tang@...el.com>, 
	Linux MM <linux-mm@...ck.org>, Cgroups <cgroups@...r.kernel.org>, 
	Paolo Abeni <pabeni@...hat.com>, "davem@...emloft.net" <davem@...emloft.net>, 
	"kuba@...nel.org" <kuba@...nel.org>, "Brandeburg, Jesse" <jesse.brandeburg@...el.com>, 
	"Srinivas, Suresh" <suresh.srinivas@...el.com>, "Chen, Tim C" <tim.c.chen@...el.com>, 
	"You, Lizhen" <lizhen.you@...el.com>, "eric.dumazet@...il.com" <eric.dumazet@...il.com>, 
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, "Li, Philip" <philip.li@...el.com>, 
	"Liu, Yujie" <yujie.liu@...el.com>
Subject: Re: [PATCH net-next 1/2] net: Keep sk->sk_forward_alloc as a proper size

On Thu, Jun 1, 2023 at 4:48 AM Zhang, Cathy <cathy.zhang@...el.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Shakeel Butt <shakeelb@...gle.com>
> > Sent: Thursday, June 1, 2023 3:45 AM
> > To: Sang, Oliver <oliver.sang@...el.com>
> > Cc: Zhang, Cathy <cathy.zhang@...el.com>; Yin, Fengwei
> > <fengwei.yin@...el.com>; Tang, Feng <feng.tang@...el.com>; Eric Dumazet
> > <edumazet@...gle.com>; Linux MM <linux-mm@...ck.org>; Cgroups
> > <cgroups@...r.kernel.org>; Paolo Abeni <pabeni@...hat.com>;
> > davem@...emloft.net; kuba@...nel.org; Brandeburg, Jesse
> > <jesse.brandeburg@...el.com>; Srinivas, Suresh
> > <suresh.srinivas@...el.com>; Chen, Tim C <tim.c.chen@...el.com>; You,
> > Lizhen <lizhen.you@...el.com>; eric.dumazet@...il.com;
> > netdev@...r.kernel.org; Li, Philip <philip.li@...el.com>; Liu, Yujie
> > <yujie.liu@...el.com>
> > Subject: Re: [PATCH net-next 1/2] net: Keep sk->sk_forward_alloc as a proper
> > size
> >
> > Hi Oliver,
> >
> > On Wed, May 31, 2023 at 04:46:08PM +0800, Oliver Sang wrote:
> > [...]
> > >
> > > we applied below patch upon v6.4-rc2, so far, we didn't spot out
> > > performance impacts of it to other tests.
> > >
> > > but we found -7.6% regression of netperf.Throughput_Mbps
> > >
> >
> > Thanks, this is what I was looking for. I will dig deeper and decide how to
> > proceed (i.e. improve this patch or work on long term approach).
>
> Hi Shakeel,
> If I understand correctly, I think the long-term goal you mentioned is to
> implement a per-memcg per-cpu cache or a percpu_counter solution, right?
> A per-memcg per-cpu cache solution can avoid the uncharge overhead and
> reduce charge overhead, while the percpu_counter solution can help avoid
> the charge overhead ultimately. It seems both are necessary and complex.
>
> The above is from memory side, regarding to our original proposal that is to
> tune the reclaim threshold from network side, Eric and you worry about that
> it might re-introduce the OOM issue. I see the following two interfaces in
> network stack, which indicate the memory usage status, so is it possible to
> tune the reclaim threshold to smaller when enter memory pressure and set
> it to 64K when leave memory pressure? How do you think?
>         void                    (*enter_memory_pressure)(struct sock *sk);
>         void                    (*leave_memory_pressure)(struct sock *sk);
>

No it is not possible to reclaim 'the threshold' when 10,000,000
sockets are alive and kept
a budget around 64KB.
We do not have a shrinker and we do not want one.
The only sensible solution is per-cpu cache.
This was done in core TCP stack, a similar solution is needed in
memcg, if memcg has to be used.