netdev - Re: [PATCH net] net: allow small head cache usage with large MAX_SKB

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Message-ID: <504a90ea-8234-4732-b4d0-ec498312dcd9@redhat.com>
Date: Wed, 12 Feb 2025 23:08:28 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
 Jakub Kicinski <kuba@...nel.org>, Simon Horman <horms@...nel.org>,
 Sabrina Dubroca <sd@...asysnail.net>
Subject: Re: [PATCH net] net: allow small head cache usage with large
 MAX_SKB_FRAGS values

On 2/12/25 9:47 PM, Eric Dumazet wrote:
> This patch still gives a warning if  MAX_TCP_HEADER < GRO_MAX_HEAD +
> 64 (in my local build)

Oops, I did not consider MAX_TCP_HEADER and GRO_MAX_HEAD could diverge.

> Why not simply use SKB_WITH_OVERHEAD(SKB_SMALL_HEAD_CACHE_SIZE) , and
> remove the 1024 value ?

With CONFIG_MAX_SKB_FRAGS=17, SKB_SMALL_HEAD_CACHE_SIZE is considerably
smaller than 1024, I feared decreasing such limit could re-introduce a
variation of the issue addressed by commit 3226b158e67c ("net: avoid 32
x truesize under-estimation for tiny skbs").

Do you feel it would be safe?

Thanks,

Paolo