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[Xen-devel] Re: Could we do immediate pte zaps in vunmap?

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: Could we do immediate pte zaps in vunmap?
From: Nick Piggin <npiggin@xxxxxxxxx>
Date: Sat, 27 Nov 2010 21:36:56 +1100
Cc: "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>
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On Fri, Nov 26, 2010 at 12:10:51AM -0800, Jeremy Fitzhardinge wrote:
> What if vm_unmap_ram() and co. immediately zeroed out the ptes, but
> lazily deferred the tlb flushes?  It seems to me there's no benefit in
> batching up the pte clearing since that can't be amortized like the tlb
> flush.

Yes that can be done.

> I think that would solve the problem we have with the interactions
> between lazy unmap and Xen.  The issue is having stray pte entries
> around (because Xen keeps track of those as part of its page-type
> mechanism), but stale tlb entries are no problem.

It would be great if that solves it.

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