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Date: Mon, 9 Feb 2009 21:19:12 +1100 From: Herbert Xu <herbert@...dor.apana.org.au> To: David Miller <davem@...emloft.net> Cc: netdev@...r.kernel.org Subject: Re: TX pre-headers... On Mon, Feb 09, 2009 at 02:14:03AM -0800, David Miller wrote: > > Indeed, I noticed needed_headroom when I set out to start coding > things up. :) > > There are all sorts of cases that won't work well, as you implicitly > suggest. For example, forwarding to a path that encapsulates to a GRE > or other type of tunnel. > > For IPSEC we're predominantly COW'ing the data anyways, so... Yes tunneling (especially when it's hidden by netfilter) is the hard part. Here's a thought, what if we had your global maximum, and every time we have to reallocate a packet because of a failed head room check, we increase the maximum by the needed amount (we should add a ceiling in case some buggy path ignores this maximum when allocating a new packet). This way even tunnels could benefit from not having to copy all the time. As a failed check should be rare (given that we're continuously increasing it) the overhead in updating the maximum should be reasonable. Cheers, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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