Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r259232:
Create own free list for each of the first 32 possible allocation sizes.
In case of 4K allocation quantum that means for allocations up to 128K.

With growth of memory fragmentation these lists may grow to quite a large
sizes (tenths and hundreds of thousands items). Having in one list items
of different sizes in worst case may require full linear list traversal,
that may be very expensive. Having lists for items of single size means
that unless user specify some alignment or border requirements (that are
very rare cases) first item found on the list should satisfy the request.

While running SPEC NFS benchmark on top of ZFS on 24-core machine with
84GB RAM this change reduces CPU time spent in vmem_xalloc() from 8%
and lock congestion spinning around it from 20% to invisible levels.
And that all is by the cost of just 26 more pointers per vmem instance.

If at some point our kernel will start to actively use KVA allocations
with odd sizes above 128K, something may need to be done to bigger lists
also.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Added sysctl to turn off calls to vmem_check().

Sponsored by: EMC / Isilon storage division
Discussed with: jeff

- Use an arbitrary but reasonably large import size for kva on architectures
that don't support superpages. This keeps the number of spans and internal
fragmentation lower.
- When the user asks for alignment from vmem_xalloc adjust the imported size
by 2*align to be certain we can satisfy the allocation. This comes at
the expense of potential failures when the backend can't supply enough
memory but could supply the requested size and alignment.

Sponsored by: EMC / Isilon Storage Division

- Add a statically allocated memguard arena since it is needed very early
on.
- Pass the appropriate flags to vmem_xalloc() when allocating space for
the arena from kmem_arena.

Sponsored by: EMC / Isilon Storage Division

Replace kernel virtual address space allocation with vmem. This provides
transparent layering and better fragmentation.

- Normalize functions that allocate memory to use kmem_*
- Those that allocate address space are named kva_*
- Those that operate on maps are named kmap_*
- Implement recursive allocation handling for kmem_arena in vmem.

Reviewed by: alc
Tested by: pho
Sponsored by: EMC / Isilon Storage Division

Remove unused argument from vmem_add1().

Reviewed by: jeff

- Add a general purpose resource allocator, vmem, from NetBSD. It was
originally inspired by the Solaris vmem detailed in the proceedings
of usenix 2001. The NetBSD version was heavily refactored for bugs
and simplicity.
- Use this resource allocator to allocate the buffer and transient maps.
Buffer cache defrags are reduced by 25% when used by filesystems with
mixed block sizes. Ultimately this may permit dynamic buffer cache
sizing on low KVA machines.

Discussed with: alc, kib, attilio
Tested by: pho
Sponsored by: EMC / Isilon Storage Division