Changes:
- Additional parameter in migrate_page_remove_references
- Various cleanups
- Credits
- Against 2.6.14-rc5-mm1 + V5 swapmig + config patch.

The intend of this patchset is to go further on the way to fully support
all the features of the existing page migration code in the
memory hotplug patchset. The attempt is to make this less intrusive
and modularize in such a way that this can be easily reviewed
and accepted upstream.

The patchset now contains more functionality but there are
some features of the hotplug patchset that are not included
and may be added later after some more community discussion.

- migration unwinding (I am not sure about this feature. May create more
  trouble than its worth)
- try_to_unmap rewrite that allows more types of pages to be migratable.
  This is correlated with migration unwinding. If we had a reliable form of
  unmapping then no unwinding would be necessary.
- arch dependent migration of the PG_arch1 bit (I have seen no application for
  it so far)
- all features not directly related to page migration (f.e. catching pages,
  only allocating certain types of allocation on removable memory etc)

This patchset depends on V5 of the Swap Migration patchset plus the
config patch.

It implements direct page migration on top of that patchset
with the same APIs supported by the swap migration patchset.

The patchset consists of six patches (only the first three are necessary to
have basic direct migration support):

1. SwapCache patch

SwapCache pages may have changed their type after lock_page().
Check for this and retry lookup if the page is no longer a SwapCache
page after lookup.

2. radix_tree_replace patch

Add replace_radix_tree (Nick: Maybe your solution is better?)

3. migrate_pages()

Basic direct migration with fallback to swap

4. buffer_migrate_pages() patch

Add filesystem dependent migration and support for the filesystems
also supported by hotplug page migration.

5. policy layer updates for direct page migration

There is a slight version mismatch going on right now since Linus tree
contains more recent nodemask support than 2.6.14-rc5-mm1. sys_migrate_pages
requires the more recent support form Paul. In order to make this work the
hacks in cpuset.h must be removed.

6. Add remove_from_swap

Slight hack around the problem of not having "force" in try_to_unmap like
the hotplug project. Use reverse mapping to replace swap pte's with real ones.
Reduces swap use.


Credits (also in mm/vsmscan.c):

Page migration was developed in the context of the memory hotplug project.
The main authors of the migration code are:

IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
Hirokazu Takahashi <taka@valinux.co.jp>
Dave Hansen <haveblue@us.ibm.com>