Original i386 log message:
Optimize the case of writing to /dev/zero, and clean up the
surrounding code a bit. Partly suggested by gwr.
I think this needs to be applied to arm26 as well.
This will allow improvements to the pmaps so that they can more easily defer expensive operations, eg tlb/cache flush, til the last possible moment.
Currently this is a no-op on most platforms, so they should see no difference.
Reviewed by Jason.