netdev - Re: [PATCH] TX_RING and packet mmap

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Message-ID: <20090421094149.GA22907@ioremap.net>
Date:	Tue, 21 Apr 2009 13:41:49 +0400
From:	Evgeniy Polyakov <zbr@...emap.net>
To:	Johann Baudy <johann.baudy@...-log.net>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>, jamal <hadi@...erus.ca>
Subject: Re: [PATCH] TX_RING and packet mmap

Hi Johann.

On Sat, Apr 18, 2009 at 11:38:48PM +0200, Johann Baudy (johann.baudy@...-log.net) wrote:
> > I think it should only be called when shared area is about to be freed
> > and not when attached skb is freed.
> During skb_linearize(). shared info is memcopied and freed in
> pskb_expand_head() if not enough memory is available in current head.
> Then, Do you expect this new destructor to be called twice? (during
> skb_linearize() and kfree_skb())

It cals skb_release_data() which should invoke shared area destructor
before being freed.

> >Thus you can put your pages into
> > fraglist and reuse them after the last reference to the shared area is
> > gone.
> 
> If my understanding is correct, skb can be linearized without calling
> skb_release_data() (if enough space is available in head). Hence, In
> this case, I will not have access to original frags[] from
> skb_shared_info destructor.

Yes, that's right.

-- 
	Evgeniy Polyakov
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