Re: [Xen-devel] Features and bug-fixes that went in Linux 3.2

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-01-12 at 17:02 +0000, Laszlo Ersek wrote:
> On 01/09/12 23:37, Ian Campbell wrote:
> > On Mon, 2012-01-09 at 22:26 +0000, James Harper wrote:
> >>>   - Initial work laid out for netback page-flipping (also called 
> >>> zero-copying).
> >>
> >> Isn't this how it used to work originally?
> >
> > Some of the original infrastructure for doing this was not upstreamable
> > (the PageForeign stuff) so while upstream netback I decided to go with a
> > simpler/less-intrusive copying mode so we could have some sort of
> > networking support in mainline.
> >
> > I've been working on re-laying the necessary infrastructure to allow for
> > page flipping/mapping mode in upstream (as well as fixing another
> > generic class of bug) -- you can see the "skb frag destructor" patches
> > on the netdev list.
> 
> (Ultimately I found it here:
> 
>      http://lwn.net/Articles/474791/
> 
> .)


The most recent posting starts at: 
http://thread.gmane.org/gmane.linux.network/217006

> Ian, do you think the NFS fix in
> 
>      http://article.gmane.org/gmane.linux.nfs/45955
> 
> for problem
> 
>      http://marc.info/?l=linux-nfs&m=122424132729720&w=2
> 
> would be technically feasible to port to 2.6.18, based on the existing 
> PageForeign stuff instead of parts 1-5 of the series?

I don't think so -- PageForeign is triggered by the last core page
reference getting dropped, but in the NFS case the running process holds
at least one so you won't actually complete until the process exits...

This is similar to the sorts of issue I described in:
http://thread.gmane.org/gmane.linux.network/217006

Ian.


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