netdev - RE: [PATCH V2,net-next, 3/3] net: mana: Add support for jumbo frame

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Date:   Wed, 12 Apr 2023 14:36:50 +0000
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     Jacob Keller <jacob.e.keller@...el.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Dexuan Cui <decui@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Paul Rosswurm <paulros@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "leon@...nel.org" <leon@...nel.org>,
        Long Li <longli@...rosoft.com>,
        "ssengar@...ux.microsoft.com" <ssengar@...ux.microsoft.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        Ajay Sharma <sharmaajay@...rosoft.com>,
        "hawk@...nel.org" <hawk@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH V2,net-next, 3/3] net: mana: Add support for jumbo frame



> -----Original Message-----
> From: Jacob Keller <jacob.e.keller@...el.com>
> Sent: Tuesday, April 11, 2023 7:13 PM
> To: Haiyang Zhang <haiyangz@...rosoft.com>; linux-hyperv@...r.kernel.org;
> netdev@...r.kernel.org
> Cc: Dexuan Cui <decui@...rosoft.com>; KY Srinivasan <kys@...rosoft.com>;
> Paul Rosswurm <paulros@...rosoft.com>; olaf@...fle.de;
> vkuznets@...hat.com; davem@...emloft.net; wei.liu@...nel.org;
> edumazet@...gle.com; kuba@...nel.org; pabeni@...hat.com;
> leon@...nel.org; Long Li <longli@...rosoft.com>;
> ssengar@...ux.microsoft.com; linux-rdma@...r.kernel.org;
> daniel@...earbox.net; john.fastabend@...il.com; bpf@...r.kernel.org;
> ast@...nel.org; Ajay Sharma <sharmaajay@...rosoft.com>;
> hawk@...nel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH V2,net-next, 3/3] net: mana: Add support for jumbo
> frame
> 
> 
> 
> On 4/7/2023 1:59 PM, Haiyang Zhang wrote:
> > During probe, get the hardware-allowed max MTU by querying the device
> > configuration. Users can select MTU up to the device limit.
> > When XDP is in use, limit MTU settings so the buffer size is within
> > one page.
> > Also, to prevent changing MTU fails, and leaves the NIC in a bad state,
> > pre-allocate all buffers before starting the change. So in low memory
> > condition, it will return error, without affecting the NIC.
> >
> 
> What happens if XDP gets enabled after MTU larger than PAGE_SIZE is set?
> Will XDP fail to enable in that case?

Yes, XDP program will fail to enable if MTU is too large.

Thanks,
- Haiyang