[PATCH] Avoid losing timer ticks when slab debug is enabled.

Patch from Manfred Spraul <manfred@colorfullife.com>

When slab debugging is enabled we're holding off interrupts for too long
(more than a jiffy), so reduce the alloc/free batching size when slab debug
is enabled.

mm/slab.c

@@ -2048,6 +2048,14 @@ static void enable_cpucache (kmem_cache_t *cachep)
 	int err;
 	int limit;
 
+	/* The head array serves three purposes:
+	 * - create a LIFO ordering, i.e. return objects that are cache-warm
+	 * - reduce the number of spinlock operations.
+	 * - reduce the number of linked list operations on the slab and 
+	 *   bufctl chains: array operations are cheaper.
+	 * The numbers are guessed, we should auto-tune as described by
+	 * Bonwick.
+	 */
 	if (cachep->objsize > PAGE_SIZE)
 		limit = 8;
 	else if (cachep->objsize > 1024)
@@ -2057,6 +2065,14 @@ static void enable_cpucache (kmem_cache_t *cachep)
 	else
 		limit = 248;
 
+#ifndef DEBUG
+	/* With debugging enabled, large batchcount lead to excessively
+	 * long periods with disabled local interrupts. Limit the 
+	 * batchcount
+	 */
+	if (limit > 32)
+		limit = 32;
+#endif
 	err = do_tune_cpucache(cachep, limit, limit/2);
 	if (err)
 		printk(KERN_ERR "enable_cpucache failed for %s, error %d.\n",