Here's a patch that optimizes out using a struct pte_chain when there's
only one mapping for that page.  It re-uses the pte_chain pointer in struct
page, with an appropriate flag.  The patch is based on Rik's latest 2.5.25
rmap patch.

I've done basic testing on it (it boots and runs simple commands).

This version of the patch uses an anonymous union, so it only builds with
gcc 3.x.  I'm working on an alternate version of the patch, but wanted to
get this one out for people to look at.

Dave McCracken

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Dave McCracken          IBM Linux Base Kernel Team      1-512-838-3059
dmccr@us.ibm.com                                        T/L   678-3059