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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Message-ID: <20161204031958.GD70461@kafai-mba.local>
Date:   Sat, 3 Dec 2016 19:19:58 -0800
From:   Martin KaFai Lau <kafai@...com>
To:     Rick Jones <rick.jones2@....com>
CC:     <netdev@...r.kernel.org>, Alexei Starovoitov <ast@...com>,
        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 Fri, Dec 02, 2016 at 04:07:09PM -0800, Rick Jones wrote:
> On 12/02/2016 03:23 PM, Martin KaFai Lau wrote:
> >When XDP prog is attached, it is currently limiting
> >MTU to be FRAG_SZ0 - ETH_HLEN - (2 * VLAN_HLEN) which is 1514
> >in x86.
> >
> >AFAICT, since mlx4 is doing one page per packet for XDP,
> >we can at least raise the MTU limitation up to
> >PAGE_SIZE - ETH_HLEN - (2 * VLAN_HLEN) which this patch is
> >doing.  It will be useful in the next patch which allows
> >XDP program to extend the packet by adding new header(s).
>
> Is mlx4 the only driver doing page-per-packet?
Sorry for the late reply.  This allocation scheme is only effective
when XDP is active.  AFAIK, only mlx4/5 supports XDP now.