netdev - Re: [PATCH RFC 0/6] copy aside frags with destructors (was [PATCH 7/9] net: add skb_orphan_frags to copy aside frags with destructors)

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Message-ID: <1336474451.14542.63.camel@zakaz.uk.xensource.com>
Date:	Tue, 8 May 2012 11:54:11 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>
Subject: Re: [PATCH RFC 0/6] copy aside frags with destructors (was [PATCH
 7/9] net: add skb_orphan_frags to copy aside frags with destructors)

On Tue, 2012-05-08 at 10:41 +0100, Michael S. Tsirkin wrote:
> On Mon, May 07, 2012 at 04:53:46PM +0300, Michael S. Tsirkin wrote:
> > > > > But I fear we're about to toss Ian into yet another rabbit hole. :-)
> > > > > 
> > > > > Let's try to converge on something quickly as I think integration of
> > > > > his work has been delayed enough as-is.
> 
> ...
> 
> > Here's a first stub at a fix. Basically to be able to modify frags on
> > the fly we must make sure the skb isn't cloned, so the moment someone
> > clones the skb we need to trigger the frag copy logic.  And this is
> > exactly what happens with SKBTX_DEV_ZEROCOPY so it seems to make sense
> > to reuse that logic.
> > 
> > The below patchset replaces patch 7
> > ([PATCH 7/9] net: add skb_orphan_frags to copy aside frags with destructors)
> > in Ian's patchset and needs to be applied there.
> > 
> > 
> > Compiled only but I'd like to hear what people think all the same
> > because it does add a couple of branches on fast path.  On the other
> > hand this makes it generic so the same logic will be reusable for packet
> > sockets (which IIRC are currently buggy in the same way as sunrpc) and
> > for adding zero copy support to tun.
> > 
> > Please comment,
> > Thanks!
> 
> Ian, just to stress, need your ack that this does what you wanted.

Sure, yesterday was a public holiday and today looks likely to be crazy
busy. I'll try and have a look later in the week.

Ian.


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