'RELENG_5_3_0_RELEASE'.

This commit was manufactured to restore the state of the 5.3-RELEASE image.

   "debug.mpsafevm" results in (almost) Giant-free execution of zero-fill
   page faults.  (Giant is held only briefly, just long enough to determine
   if there is a vnode backing the faulting address.)

   Also, condition the acquisition and release of Giant around calls to
   pmap_remove() on "debug.mpsafevm".

   The effect on performance is significant.  On my dual Opteron, I see a
   3.6% reduction in "buildworld" time.

 - Use atomic operations to update several counters in vm_fault().

wait for system wires to disappear, do so (much more trivially) by
instead only checking for system wires of user maps and not kernel maps.

Alternative by:	tor
Reviewed by:	alc

algorithm built into the map entry splay tree.  This replaces the
first_free hint in struct vm_map with two fields in vm_map_entry:
adj_free, the amount of free space following a map entry, and
max_free, the maximum amount of free space in the entry's subtree.
These fields make it possible to find a first-fit free region of a
given size in one pass down the tree, so O(log n) amortized using
splay trees.

This significantly reduces the overhead in vm_map_findspace() for
applications that mmap() many hundreds or thousands of regions, and
has a negligible slowdown (0.1%) on buildworld.  See, for example, the
discussion of a micro-benchmark titled "Some mmap observations
compared to Linux 2.6/OpenBSD" on -hackers in late October 2003.

OpenBSD adopted this approach in March 2002, and NetBSD added it in
November 2003, both with Red-Black trees.

Submitted by: Mark W. Krentel

to avoid later changes before pmap_enter() and vm_fault_prefault()
has completed.

Simplify deadlock avoidance by not blocking on vm map relookup.

In collaboration with: alc

* Allow no-fault wiring/unwiring to succeed for consistency;
  however, the wired count remains at zero, so it's a special case.

* Fix issues inside vm_map_wire() and vm_map_unwire() where the
  exact state of user wiring (one or zero) and system wiring
  (zero or more) could be confused; for example, system unwiring
  could succeed in removing a user wire, instead of being an
  error.

* Require all mappings to be unwired before they are deleted.
  When VM space is still wired upon deletion, it will be waited
  upon for the following unwire.  This makes vslock(9) work
  rather than allowing kernel-locked memory to be deleted
  out from underneath of its consumer as it would before.

(The last vestiges of the share map code were removed in revisions 1.153
and 1.159.)