netdev - Re: [PATCH net-next 2/4] mlx4: xdp: Allow raising MTU up to one page minus eth and vlan hdrs

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Date:   Sun, 04 Dec 2016 16:52:54 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Saeed Mahameed <saeedm@....mellanox.co.il>
Cc:     Alexei Starovoitov <ast@...com>, Martin KaFai Lau <kafai@...com>,
        Linux Netdev List <netdev@...r.kernel.org>,
        Brenden Blanco <bblanco@...mgrid.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH net-next 2/4] mlx4: xdp: Allow raising MTU up to one
 page minus eth and vlan hdrs

On Mon, 2016-12-05 at 01:31 +0200, Saeed Mahameed wrote:

> Alexei, we should start considering PPC archs for XDP use cases,
> demanding page per packet on those archs is a little bit heavy
> requirement

Well, 'little' is an understatement ;)

Note that PPC had serious problems before  commit bd68a2a854ad5a85f0
("net: set SK_MEM_QUANTUM to 4096")

So I suspect one page per frame will likely be a huge problem
for hosts dealing with 10^5 or more TCP sockets.

Either skb->truesize is set to 64KB and TCP window must be really tiny,
or skb->truesize is set to ~2KB and OOM is waiting to happen.