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

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Date:	Sun, 21 Oct 2007 20:34:57 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	dean gaudet <dean@...tic.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

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.

    J
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