netdev - Re: [PATCH net-next v2 3/4] virtio-net: auto-tune mergeable rx buffer size for improved performance

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Message-ID: <1389206677.31367.5.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 08 Jan 2014 10:44:37 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Michael Dalton <mwdalton@...gle.com>
Cc:	Jason Wang <jasowang@...hat.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	lf-virt <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH net-next v2 3/4] virtio-net: auto-tune mergeable rx
 buffer size for improved performance

On Wed, 2014-01-08 at 10:28 -0800, Michael Dalton wrote:
> Hi Jason,
> 
> On Tue, Jan 7, 2014 at 10:23 PM, Jason Wang <jasowang@...hat.com> wrote:
> > What's the reason that this extra space is not accounted for truesize?
> The initial rationale was that this extra space is due to
> internal fragmentation in the page frag allocator, but I agree with
> you -- this code should be changed and the extra space accounted for.
> Any internal fragmentation leading to a larger last packet allocated from
> the page should be reflected in the SKB truesize of the last packet.

Thats not a hard requirement.

Lets keep things simple and fast.

Correctness here is not mandatory, as long as we do not underestimate
truesize by a huge value like a factor of 10.

Hint :

When __netdev_alloc_frag() has to allocate a new page, because
remaining space in current page is too small, the lost hole is not
accounted to users of current page.



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