netdev - Re: [PATCH 1/4] net: add support for per-paged-fragment destructors

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Date:	Wed, 9 Nov 2011 16:25:14 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH 1/4] net: add support for per-paged-fragment destructors

On Wed, 2011-11-09 at 15:33 +0000, Michał Mirosław wrote:
> On Wed, Nov 09, 2011 at 03:02:04PM +0000, Ian Campbell wrote:
> > Entities which care about the complete lifecycle of pages which they inject
> > into the network stack via an skb paged fragment can choose to set this
> > destructor in order to receive a callback when the stack is really finished
> > with a page (including all clones, retransmits, pull-ups etc etc).
> [...]
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -139,9 +139,16 @@ struct sk_buff;
> >  
> >  typedef struct skb_frag_struct skb_frag_t;
> >  
> > +struct skb_frag_destructor {
> > +	atomic_t ref;
> > +	int (*destroy)(void *data);
> > +	void *data;
> > +};
> > +
> >  struct skb_frag_struct {
> >  	struct {
> >  		struct page *p;
> > +		struct skb_frag_destructor *destructor;
> >  	} page;
> 
> You can get rid of the data field of skb_frag_destructor: if destroy() gets
> pointer to the destroyed struct skb_frag_set_destructor, its users can
> get at containing struct via container_of() if needed and the memory
> pointed to by data won't have to be managed separately.

At the moment you can share one destructor between all the frags,
whereas data is specific to the frag. At the moment the only user is the
rpc patch which doesn't make use of this capability (i.e. it could use
container_of) but I'm not sure about other potential users yet.

> Nice work, BTW!

Thanks.

> 
> Best Regards,
> Michał Mirosław


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