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Date:   Sun, 15 Dec 2019 11:59:40 -0800
From:   Eric Dumazet <>
To:     Jakub Kicinski <>,
        Arjun Roy <>
Subject: Re: [PATCH net-next] tcp: Set rcv zerocopy hint correctly if skb last
 frag is < PAGE_SIZE.

On 12/15/19 11:22 AM, Jakub Kicinski wrote:
> On Thu, 12 Dec 2019 14:59:30 -0800, Arjun Roy wrote:
>> At present, if the last frag of paged data in a skb has < PAGE_SIZE
>> data, we compute the recv_skip_hint as being equal to the size of that
>> frag and the entire next skb.
>> Instead, just return the runt frag size as the hint.
> nit: this commit message doesn't really tell us why or what the effects
>      are going to be.

Right, I added a bit of explanation.

Basically we would hint the application to copy more bytes than needed.

Since zerocopy is best effort, this can target net-next

>> Signed-off-by: Arjun Roy <>
>> Acked-by: Soheil Hassas Yeganeh <>
>> Signed-off-by: Eric Dumazet <>
> WARNING: Missing Signed-off-by: line by nominal patch author 'Arjun Roy <>'
> You gotta send it from the same address you signed it off from.

I sent a v2 on behalf of Arjun.


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