netdev - Re: gso: Attempt to handle mega-GRO packets

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Message-ID: <20131107014724.GA28946@gondor.apana.org.au>
Date:	Thu, 7 Nov 2013 09:47:24 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	David Miller <davem@...emloft.net>,
	christoph.paasch@...ouvain.be, netdev@...r.kernel.org,
	hkchu@...gle.com, mwdalton@...gle.com, mst@...hat.com,
	Jason Wang <jasowang@...hat.com>
Subject: Re: gso: Attempt to handle mega-GRO packets

On Wed, Nov 06, 2013 at 05:03:28PM -0800, Eric Dumazet wrote:
>
> > But once the system has been running for a while, I see nothing
> > in the virtio_net code that tries to prevent fragmentation.  Once
> > fragmentation sets in, you'll be back in the terrible situation
> > that we were in prior to the coalesce patch.
> 
> There is no fragmentation, since we allocate 32Kb pages.

Say the system is fragmented sufficiently that you'll end up with
0-order pages.  In that case you'll only ever be able to coalesce
two packets.

Real systems that run for more than a day do end up with seriously
fragmented memory.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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