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

[ebiederm@xmission.com (Eric W. Biederman)]

Jeremy Fitzhardinge <jeremy@xensource.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