netdev - RE: [PATCH V3,net-next, 3/4] net: mana: Enable RX path to handle various MTU sizes

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Date:   Sat, 15 Apr 2023 14:25:29 +0000
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        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>,
        "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 V3,net-next, 3/4] net: mana: Enable RX path to handle
 various MTU sizes



> -----Original Message-----
> From: Jakub Kicinski <kuba@...nel.org>
> Sent: Friday, April 14, 2023 10:06 PM
> To: Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: linux-hyperv@...r.kernel.org; netdev@...r.kernel.org; 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;
> 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 V3,net-next, 3/4] net: mana: Enable RX path to handle
> various MTU sizes
> 
> On Wed, 12 Apr 2023 14:16:02 -0700 Haiyang Zhang wrote:
> > +	} else if (rxq->alloc_size > PAGE_SIZE) {
> > +		if (is_napi)
> > +			va = napi_alloc_frag(rxq->alloc_size);
> 
> Allocating frag larger than a page is not safe.

 I saw other drivers doing this - use napi_alloc_frag for size bigger than a page.
And it returns compound page. Why it's not safe? Should we use other allocator
when need compound pages?

> Frag allocator falls back to allocating single pages, doesn't it?

Actually I checked it. Compound page is still returned for size smaller than PAGE_SIZE,
so I used single page allocation for that.

Thanks,
- Haiyang