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[Xen-devel] Re: [patch 15/26] Xen-paravirt_ops: Add apply_to_page_range(

To: Ingo Molnar <mingo@xxxxxxx>
Subject: [Xen-devel] Re: [patch 15/26] Xen-paravirt_ops: Add apply_to_page_range() which applies a function to a pte range.
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 16 Mar 2007 10:08:43 -0700
Cc: Zachary Amsden <zach@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Ian Pratt <ian.pratt@xxxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, Andi Kleen <ak@xxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Christoph Lameter <clameter@xxxxxxx>, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
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Ingo Molnar wrote:
> nice one! I suspect we could simplify some of the less 
> performance-critical open-coded pagetable walker loops in the kernel 
> with this? (i'm not even sure it's all that much of a performance loss 
> to pass a function pointer around - would be nice to convert say 
> mprotect() to this and see the performance difference?)
>   

apply_page_to_range has the side-effect of allocating all the pagetable
levels for the address range it walks.  Xen uses this to populate
pagetables (for example, build out the pagetable, and let the hypervisor
plug a mapping into the pte page).

If that's OK for the other uses, then it should be good.

    J

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