Re: [Xen-devel] [PATCH 0/3] make ballooned out pages have a valid mapping at all times

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2013-07-22 at 16:35 +0100, Stefano Stabellini wrote:
> On Mon, 22 Jul 2013, David Vrabel wrote:
> > On 21/07/13 18:32, Stefano Stabellini wrote:
> > > Hi all,
> > > this patch series limits problems caused by tcp retransmits on NFS when
> > > the original block pages were mapped from a foreign domain and now the
> > > mapping is gone.
> > > 
> > > It accomplishes the goal by:
> > > 
> > > 1) mapping all ballooned out pages to a "balloon_trade_page";
> > > 2) making sure that once a grant is unmapped, the original mapping to
> > > balloon_trade_page is restored atomically.
> > 
> > I think this can be fixed without any hypervisor-side changes, although
> > hypervisor changes will allow you to do it more efficiently.
> > 
> > Use a per-CPU set of trade pages.
> > 
> > Note MFN of this CPU's trade page (trade_mfn).
> > Do the grant_unmap_and_replace(), (trade page mapping's MFN is cleared
> > but this is ok as nothing is accessing the page via this mapping).
> > update_va_mapping on trade page VA to set its MFN to trade_mfn.
> 
> I am going to go for this, avoiding any Xen side changes.

Oops, I won't bother responding to the rest of your replies to my
comments on the patches then. You can safely ignore the couple I just
sent.

Ian.


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