[PATCH] Allow arch override for kmem_bufctl_t

[Manfred Spraul <manfred@colorfullife.com>]

Hi Andrew,

The slab allocator keeps track of the free objects in a slab with a 
linked list of integers (typedef'ed to kmem_bufctl_t). Right now 
unsigned int is used for kmem_bufctl_t, i.e. 4 bytes per-object overhead.
The attached patch allows an arch override for this type: Theoretically, 
unsigned short is sufficient for kmem_bufctl_t and this would reduce the 
per-object overhead to 2 bytes. But some archs cannot operate on 16-bit 
values efficiently, thus it's not possible to switch everyone to ushort. 
The patch switches i386, the port maintainers should switch their arch 
if there are no problems with 16-bit quantities. All accesses to 
kmem_bufctl_t are under a per-cache spinlock and not in the hottest path.

Could you apply it to -mm?

--
    Manfred