There's been a fair amount of discussion about the advantages of doing
object-based rmap.  I've been looking into it, and we have the pieces to do
it for file-backed objects, ie the ones that have a real address_space
object pointed to from struct page.  The stumbling block has always been
anonymous pages.

At Martin Bligh's suggestion, I coded up an object-based implementation for
non-anon pages while leaving the pte_chain code intact for anon pages.  My
fork/exit microbenchmark shows roughly 50% improvement for tasks that are
composes of file-backed and/or shared pages.  This is the code that Martin
included in 2.5.62-mjb2 and reported his performance results on.

Anyway, here's the patch if anyone wants to check it out.

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