uvm_object::vmobjlock

[Mindaugas Rasiukevicius <rmind%netbsd.org@localhost>]

Hello,

Unless anyone objects, I would like to change struct uvm_object::vmobjlock to
be dynamically allocated with mutex_obj_alloc().  It allows us to:  1) share
the lock among objects by holding a reference  2) avoid false-sharing on locks.
Note that struct vnode::v_interlock becomes a pointer, which means a chunk of
mechanical changes.

-- 
Mindaugas