mm/slab: alternative implementation for DEBUG_SLAB_LEAK

mm/slab: alternative implementation for DEBUG_SLAB_LEAK

DEBUG_SLAB_LEAK is a debug option.  It's current implementation requires
status buffer so we need more memory to use it.  And, it cause kmem_cache
initialization step more complex.

To remove this extra memory usage and to simplify initialization step,
this patch implement this feature with another way.

When user requests to get slab object owner information, it marks that
getting information is started.  And then, all free objects in caches are
flushed to corresponding slab page.  Now, we can distinguish all freed
object so we can know all allocated objects, too.  After collecting slab
object owner information on allocated objects, mark is checked that there
is no free during the processing.  If true, we can be sure that our
information is correct so information is returned to user.

Although this way is rather complex, it has two important benefits
mentioned above.  So, I think it is worth changing.

There is one drawback that it takes more time to get slab object owner
information but it is just a debug option so it doesn't matter at all.

To help review, this patch implements new way only.  Following patch will
remove useless code.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>