slub: Add method to verify memory is not freed

This is for tracking down suspect memory usage.

Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

diff --cc include/linux/slub_def.h
Simple merge

diff --cc mm/slub.c
Simple merge