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

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Message-ID: <1338838185.2760.1899.camel@edumazet-glaptop>
Date:	Mon, 04 Jun 2012 21:29:45 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.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, 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



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