Lower minimum objects/slab threshold

As long as we can fit a minimum of one object/slab there's no reason
to prevent the creation of the cache.  This effectively pushes the
maximum object size up to 32MB.  The splat cache tests were extended
accordingly to verify this functionality.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

include/sys/kmem.h

@@ -395,7 +395,7 @@ extern struct rw_semaphore spl_kmem_cache_sem;
 #define SPL_KMEM_CACHE_DELAY		15	/* Minimum slab release age */
 #define SPL_KMEM_CACHE_REAP		0	/* Default reap everything */
 #define SPL_KMEM_CACHE_OBJ_PER_SLAB	16	/* Target objects per slab */
-#define SPL_KMEM_CACHE_OBJ_PER_SLAB_MIN	8	/* Minimum objects per slab */
+#define SPL_KMEM_CACHE_OBJ_PER_SLAB_MIN	1	/* Minimum objects per slab */
 #define SPL_KMEM_CACHE_ALIGN		8	/* Default object alignment */
 
 #define POINTER_IS_VALID(p)		0	/* Unimplemented */

module/splat/splat-kmem.c

@@ -799,6 +799,10 @@ splat_kmem_test6(struct file *file, void *arg)
 	if (rc)
 		return rc;
 
+	rc = splat_kmem_cache_test(file, arg, name, 16*1024*1024, 0, KMC_VMEM);
+	if (rc)
+		return rc;
+
 	/* Off slab (default + kmem + vmem) */
 	rc = splat_kmem_cache_test(file, arg, name, 256*1024, 0, KMC_OFFSLAB);
 	if (rc)
@@ -811,6 +815,11 @@ splat_kmem_test6(struct file *file, void *arg)
 
 	rc = splat_kmem_cache_test(file, arg, name, 1024*1024, 0,
 	    KMC_VMEM | KMC_OFFSLAB);
+	if (rc)
+		return rc;
+
+	rc = splat_kmem_cache_test(file, arg, name, 16*1024*1024, 0,
+	    KMC_VMEM | KMC_OFFSLAB);
 
 	return rc;
 }