netdev - Re: [PATCH net-next] net: netdev_alloc_skb() use build

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Date:	Mon, 4 Jun 2012 22:43:31 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Willy Tarreau <w@....eu>, David Miller <davem@...emloft.net>,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: netdev_alloc_skb() use build_skb()

On Mon, Jun 04, 2012 at 09:29:45PM +0200, Eric Dumazet wrote:
> On Mon, 2012-06-04 at 21:16 +0300, Michael S. Tsirkin wrote:
> 
> > Yes but if a tcp socket then hangs on, on one of the fragments,
> > while the other has been freed, the whole page is still
> > never reused, right?
> > 
> > Doesn't this mean truesize should be 4K?
> > 
> 
> Yes, or more exactly PAGE_SIZE, but then performance would really go
> down on machines with 64KB pages.
> Maybe we should make the whole frag
> head idea enabled only for PAGE_SIZE=4096.
> 
> Not sure we want to track precise truesize, as the minimum truesize is
> SKB_DATA_ALIGN(length + NET_SKB_PAD) + SKB_DATA_ALIGN(sizeof(struct
> skb_shared_info)) (64 + 64 + 320) = 448
> 
> Its not like buggy drivers that used truesize = length
> 
> 

Interesting. But where's the threshold?

-- 
MST
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