mm/slab: do not change cache size if debug pagealloc isn't possible

mm/slab: do not change cache size if debug pagealloc isn't possible

We can fail to setup off slab in some conditions.  Even in this case,
debug pagealloc increases cache size to PAGE_SIZE in advance and it is
waste because debug pagealloc cannot work for it when it isn't the off
slab.  To improve this situation, this patch checks first that this
cache with increased size is suitable for off slab.  It actually
increases cache size when it is suitable for off-slab, so possible waste
is removed.

Signed-off-by: Joonsoo Kim <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Jesper Dangaard Brouer <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>