linux-kernel - Re: [PATCH net-next v6 4/5] net: gro: remove unnecessary df checks

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Message-ID: <c557acda-ad4e-4f07-a210-99c3de5960e2@redhat.com>
Date: Thu, 18 Sep 2025 10:10:18 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Richard Gobert <richardbgobert@...il.com>, netdev@...r.kernel.org,
 ecree.xilinx@...il.com, willemdebruijn.kernel@...il.com
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 horms@...nel.org, corbet@....net, saeedm@...dia.com, tariqt@...dia.com,
 mbloch@...dia.com, leon@...nel.org, dsahern@...nel.org,
 ncardwell@...gle.com, kuniyu@...gle.com, shuah@...nel.org, sdf@...ichev.me,
 aleksander.lobakin@...el.com, florian.fainelli@...adcom.com,
 alexander.duyck@...il.com, linux-kernel@...r.kernel.org,
 linux-net-drivers@....com
Subject: Re: [PATCH net-next v6 4/5] net: gro: remove unnecessary df checks

On 9/16/25 4:48 PM, Richard Gobert wrote:
> Currently, packets with fixed IDs will be merged only if their
> don't-fragment bit is set. This restriction is unnecessary since
> packets without the don't-fragment bit will be forwarded as-is even
> if they were merged together. The merged packets will be segmented
> into their original forms before being forwarded, either by GSO or
> by TSO. The IDs will also remain identical unless NETIF_F_TSO_MANGLEID
> is set, in which case the IDs can become incrementing, which is also fine.
> 
> Note that IP fragmentation is not an issue here, since packets are
> segmented before being further fragmented. Fragmentation happens the
> same way regardless of whether the packets were first merged together.

I agree with Willem, that an explicit assertion somewhere (in
ip_do_fragmentation?!?) could be useful.

Also I'm not sure that "packets are segmented before being further
fragmented" is always true for the OVS forwarding scenario.

/P