linux-kernel - Re: Interaction between Xen and XFS: stray RW mappings

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Date:	Sun, 21 Oct 2007 21:28:32 -0700 (PDT)
From:	dean gaudet <dean@...tic.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
cc:	Nick Piggin <nickpiggin@...oo.com.au>, David Chinner <dgc@....com>,
	xfs@....sgi.com, Xen-devel <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mark Williamson <mark.williamson@...cam.ac.uk>,
	Morten Bøgeskov <xen-users@...ten.bogeskov.dk>,
	xfs-masters@....sgi.com
Subject: Re: Interaction between Xen and XFS: stray RW mappings

On Sun, 21 Oct 2007, Jeremy Fitzhardinge wrote:

> dean gaudet wrote:
> > On Mon, 15 Oct 2007, Nick Piggin wrote:
> >
> >   
> >> Yes, as Dave said, vmap (more specifically: vunmap) is very expensive
> >> because it generally has to invalidate TLBs on all CPUs.
> >>     
> >
> > why is that?  ignoring 32-bit archs we have heaps of address space 
> > available... couldn't the kernel just burn address space and delay global 
> > TLB invalidate by some relatively long time (say 1 second)?
> >   
> 
> Yes, that's precisely the problem.  xfs does delay the unmap, leaving
> stray mappings, which upsets Xen.

sounds like a bug in xen to me :)

-dean
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