From: Manfred Spraul <manfred@colorfullife.com>

Now that slab supports monster objects (up to 32MB) for !CONFIG_MMU we really
don't want to keep spare instances of them in the slab head arrays.

- limit head array sizes for huge slab caches to one object per cpu.

- round the batch count up for default head array sizing - batch count 0 is
  illegal.