slab allocators: Remove SLAB_DEBUG_INITIAL flag

I have never seen a use of SLAB_DEBUG_INITIAL.  It is only supported by
SLAB.

I think its purpose was to have a callback after an object has been freed
to verify that the state is the constructor state again?  The callback is
performed before each freeing of an object.

I would think that it is much easier to check the object state manually
before the free.  That also places the check near the code object
manipulation of the object.

Also the SLAB_DEBUG_INITIAL callback is only performed if the kernel was
compiled with SLAB debugging on.  If there would be code in a constructor
handling SLAB_DEBUG_INITIAL then it would have to be conditional on
SLAB_DEBUG otherwise it would just be dead code.  But there is no such code
in the kernel.  I think SLUB_DEBUG_INITIAL is too problematic to make real
use of, difficult to understand and there are easier ways to accomplish the
same effect (i.e.  add debug code before kfree).

There is a related flag SLAB_CTOR_VERIFY that is frequently checked to be
clear in fs inode caches.  Remove the pointless checks (they would even be
pointless without removeal of SLAB_DEBUG_INITIAL) from the fs constructors.

This is the last slab flag that SLUB did not support.  Remove the check for
unimplemented flags from SLUB.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 10 deletions

diff --git a/mm/slub.c b/mm/slub.c
index 79940e98e5e6..bd86182e595e 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -97,9 +97,6 @@
  *
  * - Support PAGE_ALLOC_DEBUG. Should be easy to do.
  *
- * - SLAB_DEBUG_INITIAL is not supported but I have never seen a use of
- *   it.
- *
  * - Variable sizing of the per node arrays
  */
 
@@ -126,11 +123,6 @@
 #endif
 
 /*
- * Flags from the regular SLAB that SLUB does not support:
- */
-#define SLUB_UNIMPLEMENTED (SLAB_DEBUG_INITIAL)
-
-/*
  * Mininum number of partial slabs. These will be left on the partial
  * lists even if they are empty. kmem_cache_shrink may reclaim them.
  */
@@ -1748,8 +1740,6 @@ static int kmem_cache_open(struct kmem_cache *s, gfp_t gfpflags,
         s->flags = flags;
         s->align = align;
 
-        BUG_ON(flags & SLUB_UNIMPLEMENTED);
-
         /*
          * The page->offset field is only 16 bit wide. This is an offset
          * in units of words from the beginning of an object. If the slab