netdev - Re: [PATCH net-next] net: pskb_trim_rcsum() and CHECKSUM

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Message-Id: <20180419.134532.668231899611153609.davem@davemloft.net>
Date:   Thu, 19 Apr 2018 13:45:32 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next] net: pskb_trim_rcsum() and CHECKSUM_COMPLETE
 are friends

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 18 Apr 2018 11:43:15 -0700

> After working on IP defragmentation lately, I found that some large
> packets defeat CHECKSUM_COMPLETE optimization because of NIC adding
> zero paddings on the last (small) fragment.
> 
> While removing the padding with pskb_trim_rcsum(), we set skb->ip_summed
> to CHECKSUM_NONE, forcing a full csum validation, even if all prior
> fragments had CHECKSUM_COMPLETE set.

Oops.

> We can instead compute the checksum of the part we are trimming,
> usually smaller than the part we keep.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Looks good, applied, thanks Eric.