On Wed, 26 Jul 2006, Pekka Enberg wrote:
> On 7/26/06, Christoph Lameter <[email protected]> wrote:
> > Your patch only deals with ARCH_SLAB_MINALIGN. kmem_cache_create() never
> > uses ARCH_KMALLOC_MINALIGN only kmem_cache_init() does by passing it to
> > kmem_cache_create. ARCH_KMALLOC_MINALIGN will still be ignored.
>
> Yes, in which case the caller mandated align will be, well,
> ARCH_KMALLOC_MINALIGN. The patch changes kmem_cache_create to respect
> caller mandated alignment too.
As far as I understood Heiko s390 does not set ARCH_SLAB_MINALIGN
because they do not want alignent for all caches.
The following patch adds an option SLAB_DEBUG_OVERRIDE to switch off
debugging if its on by default. S390 would have to set ARCH_KMALLOC_FLAGS
to SLAB_DEBUG_OVERRIDE. The flag will then be passed in
kmem_cache_init to kmem_cache_create(). This approach also preserves the
existing slab behavior for all other archs.
Index: linux-2.6/include/linux/slab.h
===================================================================
--- linux-2.6.orig/include/linux/slab.h 2006-07-26 05:14:33.000000000 -0700
+++ linux-2.6/include/linux/slab.h 2006-07-26 05:15:08.000000000 -0700
@@ -46,6 +46,7 @@ typedef struct kmem_cache kmem_cache_t;
#define SLAB_PANIC 0x00040000UL /* panic if kmem_cache_create() fails */
#define SLAB_DESTROY_BY_RCU 0x00080000UL /* defer freeing pages to RCU */
#define SLAB_MEM_SPREAD 0x00100000UL /* Spread some memory over cpuset */
+#define SLAB_DEBUG_OVERRIDE 0x00200000UL /* Do not debug this slab */
/* flags passed to a constructor func */
#define SLAB_CTOR_CONSTRUCTOR 0x001UL /* if not set, then deconstructor */
Index: linux-2.6/mm/slab.c
===================================================================
--- linux-2.6.orig/mm/slab.c 2006-07-26 05:13:59.000000000 -0700
+++ linux-2.6/mm/slab.c 2006-07-26 05:17:59.000000000 -0700
@@ -2055,8 +2055,11 @@ kmem_cache_create (const char *name, siz
* above the next power of two: caches with object sizes just above a
* power of two have a significant amount of internal fragmentation.
*/
- if (size < 4096 || fls(size - 1) == fls(size-1 + 3 * BYTES_PER_WORD))
- flags |= SLAB_RED_ZONE | SLAB_STORE_USER;
+
+ if (!(flags & DEBUG_OVERRIDE) &&
+ size < 4096 ||
+ (fls(size - 1) == fls(size-1 + 3 * BYTES_PER_WORD)))
+ flags |= SLAB_RED_ZONE | SLAB_STORE_USER;
if (!(flags & SLAB_DESTROY_BY_RCU))
flags |= SLAB_POISON;
#endif
-
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