netdev - Re: [PATCH net] udp: fix memory schedule error

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Date:   Tue, 21 Feb 2023 13:35:35 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Jason Xing <kerneljasonxing@...il.com>,
        willemdebruijn.kernel@...il.com, davem@...emloft.net,
        dsahern@...nel.org, kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net] udp: fix memory schedule error

On Tue, Feb 21, 2023 at 1:27 PM Paolo Abeni <pabeni@...hat.com> wrote:
>
> On Tue, 2023-02-21 at 19:03 +0800, Jason Xing wrote:
> > From: Jason Xing <kernelxing@...cent.com>
> >
> > Quoting from the commit 7c80b038d23e ("net: fix sk_wmem_schedule()
> > and sk_rmem_schedule() errors"):
> >
> > "If sk->sk_forward_alloc is 150000, and we need to schedule 150001 bytes,
> > we want to allocate 1 byte more (rounded up to one page),
> > instead of 150001"
>
> I'm wondering if this would cause measurable (even small) performance
> regression? Specifically under high packet rate, with BH and user-space
> processing happening on different CPUs.
>
> Could you please provide the relevant performance figures?
>
> Thanks!
>
> Paolo
>

Probably not a big deal.

TCP skb truesize can easily reach 180 KB, but for UDP it's 99% below
or close to a 4K page.

I doubt this change makes any difference for UDP.