netdev - Re: [RFC] allow skb->head to point/alias to first skb frag

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Message-ID: <1335443554.2775.33.camel@edumazet-glaptop>
Date:	Thu, 26 Apr 2012 14:32:34 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Maciej Żenczykowski <maze@...gle.com>
Cc:	David Miller <davem@...emloft.net>, ilpo.jarvinen@...sinki.fi,
	rick.jones2@...com, netdev@...r.kernel.org, therbert@...gle.com,
	ncardwell@...gle.com, ycheng@...gle.com
Subject: Re: [RFC] allow skb->head to point/alias to first skb frag

On Thu, 2012-04-26 at 03:09 -0700, Maciej Żenczykowski wrote:
> it would be very useful if there was an api for freeing skb->head memory...
> 
> I've fooled around with a single memory buffer for both the head and
> the data and seen huge performance wins under heavy packet load (half
> the amount of malloc/free), but could never quite get it to be 100%
> stable.

My patch is almost ready, and seems very good.

I added a param to skb_build() to tell the memory comes from a (sub)page

tg3 uses the new thing.

GRO does the correct merging.

(by the way, I noticed GRO lies about skb truesize... since it
accumulates frag lengths instead of allocated space... with a 1448/2048
mismatch for MTU=1500)

And this apparently solves my slub performance issue I had on my dual
quad core machine, since I no longer hit slub slow path.



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