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

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

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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