linux-kernel - Re: [PATCH v2] tcp: splice as many packets as possible at once

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Message-ID: <20090203121836.GA23300@ioremap.net>
Date:	Tue, 3 Feb 2009 15:18:36 +0300
From:	Evgeniy Polyakov <zbr@...emap.net>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Jarek Poplawski <jarkao2@...il.com>,
	David Miller <davem@...emloft.net>, w@....eu,
	dada1@...mosbay.com, ben@...s.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	jens.axboe@...cle.com
Subject: Re: [PATCH v2] tcp: splice as many packets as possible at once

On Tue, Feb 03, 2009 at 11:12:09PM +1100, Herbert Xu (herbert@...dor.apana.org.au) wrote:
> The only change we need to make is at receive time.  Instead of
> always pushing the received skb into the stack, we should try to
> allocate a linear replacement skb, and if that fails, allocate
> a fragmented skb and copy the data into it.  That way we can
> always push a linear skb back into the ring buffer.

Yes, that's was the part about 'reserve' buffer for the sockets you cut
:)

I agree that this will work and will be better than nothing, but copying
9kb into 3 pages is rather CPU hungry operation, and I think (but have
no numbers though) that system will behave faster if MTU is reduced to
the standard one.
Another solution is to have a proper allocator which will be able to
defragment the data, if talking about the alternatives to the drop.

So:
1. copy the whole jumbo skb into fragmented one
2. reduce the MTU
3. rely on the allocator

For the 'good' hardware and drivers nothing from the above is really needed.

-- 
	Evgeniy Polyakov
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