Move map relookup into its own function.

[jeff]

Summary

The map revalidation is hopefully rare so we could possibly even noinline or predict_false() the call.

[kib]

sys/vm/vm_fault.c

810

You could reduce indent below by doing

if (fs->map->timestamp == fs->map_generation)
           return (KERN_SUCCESS);

there

826

What is KERN_RESTART ?

[jeff]

sys/vm/vm_fault.c

810

Yeah I also prefer to lessen indent and have more early returns. I can do that.

826

I meant to include that in this diff. I just added it to the list of vm errors. I am using KERN_RESOURCE_SHORTAGE to mean restart without fault_deallocate() and KERN_RESTART to mean restart with fault_deallocate(). It significantly reduces the number of places that call deallocate() and makes the error handling a little bit simpler.

[jeff]

Decrease indent. Remove dead comment. Add missing KERN_RESTART define.