linux-kernel - Re: [PATCH 1 of 13] Add apply_to_page_range() which applies a function to a pte range

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Message-ID: <m1ejw0zmic.fsf@ebiederm.dsl.xmission.com>
Date:	Tue, 01 Aug 2006 06:08:43 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Jeremy Fitzhardinge <jeremy@...source.com>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org,
	Chris Wright <chrisw@...s-sol.org>,
	Christian Limpach <Christian.Limpach@...cam.ac.uk>,
	Christoph Lameter <clameter@....com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Gerd Hoffmann <kraxel@...e.de>,
	Hollis Blanchard <hollisb@...ibm.com>,
	Ian Pratt <ian.pratt@...source.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Zachary Amsden <zach@...are.com>
Subject: Re: [PATCH 1 of 13] Add apply_to_page_range() which applies a function to a pte range

Jeremy Fitzhardinge <jeremy@...source.com> writes:

> 2 files changed, 99 insertions(+)
> include/linux/mm.h |    5 ++
> mm/memory.c        |   94 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>
>
> 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()).

- You don't handle huge pages.  For a generic function
  that sounds like a problem.
- I believe there is a reason the kernel doesn't already have
  a function like this.  I seem to recall there being efficiency
  and fast path arguments.
- Placing this code in mm/memory.c without a common consumer is
  pure kernel bloat for everyone who doesn't use this function,
  which is just about everyone.

Eric
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