PERFORCE change 155554 for review

[Alan Cox]

Mayur wrote:
> Hi Ed,
> This work is not targeted to reduce the contention but this seems an 
> interesting problem. Will look in to it.
>

Have a look at pmap_enter() and pmap_remove_pages() and more generally 
the use of the page queues mutex to synchronize access to the per-page 
pv list in the pmap.  A simple and (likely) productive first step would 
be to introduce a new mutex in the pmap for synchronizing access to the 
per-page pv lists.

The tricky part is that the pmap functions sometimes manipulate other 
per-page fields, like "dirty", that are also synchronized by the page 
queues lock.

If you want to undertake this, I would be very supportive.

Regards,
Alan