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xen-devel
[Xen-devel] Re: [patch 11/21] Xen-paravirt: Add apply_to_page_range() wh
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To: |
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [patch 11/21] Xen-paravirt: Add apply_to_page_range() which applies a function to a pte range. |
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From: |
Nick Piggin <nickpiggin@xxxxxxxxxxxx> |
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Date: |
Fri, 16 Feb 2007 18:31:14 +1100 |
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Cc: |
Zachary Amsden <zach@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Ian Pratt <ian.pratt@xxxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, Andi Kleen <ak@xxxxxx>, David Rientjes <rientjes@xxxxxxxxxx>, Christoph Lameter <clameter@xxxxxxx>, Linux Memory Management <linux-mm@xxxxxxxxx>, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx> |
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Fri, 16 Feb 2007 05:34:56 -0800 |
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Andrew Morton wrote:
On Thu, 15 Feb 2007 18:25:00 -0800 Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
Add a new mm function apply_to_page_range() which applies a given
function to every pte in a given virtual address range in a given mm
structure. This is a generic alternative to cut-and-pasting the Linux
idiomatic pagetable walking code in every place that a sequence of
PTEs must be accessed.
Although this interface is intended to be useful in a wide range of
situations, it is currently used specifically by several Xen
subsystems, for example: to ensure that pagetables have been allocated
for a virtual address range, and to construct batched special
pagetable update requests to map I/O memory (in ioremap()).
There was some discussion about this sort of thing last week. The
consensus was that it's better to run the callback against a whole pmd's
worth of ptes, mainly to amortise the callback's cost (a lot).
It was implemented in
ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.20/2.6.20-mm1/broken-out/smaps-extract-pmd-walker-from-smaps-code.patch
Speaking of that patch, I missed the discussion, but I'd hope it doesn't
go upstream in its current form.
We now have one way of walking range of ptes. The code may be duplicated a
few times, but it is simple, we know how it works, and it is easy to get
right because everyone does the same thing.
We used to have about a dozen slightly different ways of doing this until
Hugh spent the effort to standardise it all. Isn't it nice?
If we want an ever-so-slightly lower performing interface for those paths
that don't care to count every cycle -- which I think is a fine idea BTW
-- it should be implemented in mm/memory.c and it should use our standard
form of pagetable walking.
--
SUSE Labs, Novell Inc.
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