linux-kernel - Re: [patch 11/21] Xen-paravirt: Add apply_to_page_range() which applies a function to a pte range.

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Message-Id: <20070215223727.6819f962.akpm@linux-foundation.org>
Date:	Thu, 15 Feb 2007 22:37:27 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Andi Kleen <ak@....de>, linux-kernel@...r.kernel.org,
	virtualization@...ts.osdl.org, xen-devel@...ts.xensource.com,
	Chris Wright <chrisw@...s-sol.org>,
	Zachary Amsden <zach@...are.com>,
	Ian Pratt <ian.pratt@...source.com>,
	Christian Limpach <Christian.Limpach@...cam.ac.uk>,
	Christoph Lameter <clameter@....com>
Subject: Re: [patch 11/21] Xen-paravirt: Add apply_to_page_range() which
 applies a function to a pte range.

On Thu, 15 Feb 2007 18:25:00 -0800 Jeremy Fitzhardinge <jeremy@...p.org> 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
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