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[Xen-devel] Re: Interaction between Xen and XFS: stray RW mappings

To: dean gaudet <dean@xxxxxxxxxx>
Subject: [Xen-devel] Re: Interaction between Xen and XFS: stray RW mappings
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Sun, 21 Oct 2007 20:34:57 -0700
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Morten , David Chinner <dgc@xxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Bøgeskov <xen-users@xxxxxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, xfs-masters@xxxxxxxxxxx, Mark Williamson <mark.williamson@xxxxxxxxxxxx>
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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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