[PATCH RFC 1/8] mm, slab: refactor slab_min/max_order handling

[Vlastimil Babka (SUSE)]

Setting slab_min_order and slab_max_order as boot-time parameters
currently has several not so great aspects:

- slab_min_order is not checked against MAX_PAGE_ORDER
- slab_min_order can raise slab_max_order
- processing requires custom callbacks, their execution order
  depends on the order of boot time parameters specified
- upcoming SLUB_TINY changes would be more complicated

Instead of custom callbacks, introduce __initdata variables that hold
the boot-time parameter values (if given). All inputs are then evaluated
deterministically in kmem_cache_init(). slab_min_order is always capped
at slab_max_order and cannot raise it.

debug_guardpage_minorder() still overrides any given boot time params,
but it could be changed if there's a use case.

While at it, rename the slub_min/max_order variables and
slub_min_objects to have a "slab_" prefix instead, as their values
determine the sizing of slabs, and the "slub_" prefix already became
deprecated also for the boot-time parameters.

Signed-off-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>
---
 mm/slub.c | 84 ++++++++++++++++++++++++---------------------------------------
 1 file changed, 32 insertions(+), 52 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 96dca4846b4e..a107a111c75e 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -7598,10 +7598,17 @@ EXPORT_SYMBOL(kmem_cache_alloc_bulk_noprof);
  * and increases the number of allocations possible without having to
  * take the list_lock.
  */
-static unsigned int slub_min_order;
-static unsigned int slub_max_order =
+static unsigned int slab_min_order;
+static unsigned int slab_max_order =
 	IS_ENABLED(CONFIG_SLUB_TINY) ? 1 : PAGE_ALLOC_COSTLY_ORDER;
-static unsigned int slub_min_objects;
+static unsigned int slab_min_objects;
+
+/*
+ * Store values set by boot-time parameters, to be evaluated in
+ * kmem_cache_init(). UINT_MAX means they were not set, as 0 is a valid value.
+ */
+static unsigned int slab_min_order_param __initdata = UINT_MAX;
+static unsigned int slab_max_order_param __initdata = UINT_MAX;
 
 /*
  * Calculate the order of allocation given an slab object size.
@@ -7655,7 +7662,7 @@ static inline int calculate_order(unsigned int size)
 	unsigned int max_objects;
 	unsigned int min_order;
 
-	min_objects = slub_min_objects;
+	min_objects = slab_min_objects;
 	if (!min_objects) {
 		/*
 		 * Some architectures will only update present cpus when
@@ -7672,10 +7679,10 @@ static inline int calculate_order(unsigned int size)
 		min_objects = 4 * (fls(nr_cpus) + 1);
 	}
 	/* min_objects can't be 0 because get_order(0) is undefined */
-	max_objects = max(order_objects(slub_max_order, size), 1U);
+	max_objects = max(order_objects(slab_max_order, size), 1U);
 	min_objects = min(min_objects, max_objects);
 
-	min_order = max_t(unsigned int, slub_min_order,
+	min_order = max_t(unsigned int, slab_min_order,
 			  get_order(min_objects * size));
 	if (order_objects(min_order, size) > MAX_OBJS_PER_PAGE)
 		return get_order(size * MAX_OBJS_PER_PAGE) - 1;
@@ -7696,9 +7703,9 @@ static inline int calculate_order(unsigned int size)
 	 * long as at least single object fits within slab_max_order.
 	 */
 	for (unsigned int fraction = 16; fraction > 1; fraction /= 2) {
-		order = calc_slab_order(size, min_order, slub_max_order,
+		order = calc_slab_order(size, min_order, slab_max_order,
 					fraction);
-		if (order <= slub_max_order)
+		if (order <= slab_max_order)
 			return order;
 	}
 
@@ -8268,50 +8275,14 @@ void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab)
  *		Kmalloc subsystem
  *******************************************************************/
 
-static int __init setup_slub_min_order(const char *str, const struct kernel_param *kp)
-{
-	int ret;
-
-	ret = kstrtouint(str, 0, &slub_min_order);
-	if (ret)
-		return ret;
+core_param(slab_min_order, slab_min_order_param, uint, 0);
+core_param(slub_min_order, slab_min_order_param, uint, 0);
 
-	if (slub_min_order > slub_max_order)
-		slub_max_order = slub_min_order;
+core_param(slab_max_order, slab_max_order_param, uint, 0);
+core_param(slub_max_order, slab_max_order_param, uint, 0);
 
-	return 0;
-}
-
-static const struct kernel_param_ops param_ops_slab_min_order __initconst = {
-	.set = setup_slub_min_order,
-};
-__core_param_cb(slab_min_order, &param_ops_slab_min_order, &slub_min_order, 0);
-__core_param_cb(slub_min_order, &param_ops_slab_min_order, &slub_min_order, 0);
-
-static int __init setup_slub_max_order(const char *str, const struct kernel_param *kp)
-{
-	int ret;
-
-	ret = kstrtouint(str, 0, &slub_max_order);
-	if (ret)
-		return ret;
-
-	slub_max_order = min_t(unsigned int, slub_max_order, MAX_PAGE_ORDER);
-
-	if (slub_min_order > slub_max_order)
-		slub_min_order = slub_max_order;
-
-	return 0;
-}
-
-static const struct kernel_param_ops param_ops_slab_max_order __initconst = {
-	.set = setup_slub_max_order,
-};
-__core_param_cb(slab_max_order, &param_ops_slab_max_order, &slub_max_order, 0);
-__core_param_cb(slub_max_order, &param_ops_slab_max_order, &slub_max_order, 0);
-
-core_param(slab_min_objects, slub_min_objects, uint, 0);
-core_param(slub_min_objects, slub_min_objects, uint, 0);
+core_param(slab_min_objects, slab_min_objects, uint, 0);
+core_param(slub_min_objects, slab_min_objects, uint, 0);
 
 #ifdef CONFIG_NUMA
 static int __init setup_slab_strict_numa(const char *str, const struct kernel_param *kp)
@@ -8684,8 +8655,17 @@ void __init kmem_cache_init(void)
 
 	slab_obj_ext_has_codetag_init();
 
+	if (slab_max_order_param <= MAX_PAGE_ORDER)
+		slab_max_order = slab_max_order_param;
+
+	if (slab_min_order_param <= MAX_PAGE_ORDER)
+		slab_min_order = slab_min_order_param;
+
 	if (debug_guardpage_minorder())
-		slub_max_order = 0;
+		slab_max_order = 0;
+
+	if (slab_min_order > slab_max_order)
+		slab_min_order = slab_max_order;
 
 	/* Inform pointer hashing choice about slub debugging state. */
 	hash_pointers_finalize(__slub_debug_enabled());
@@ -8736,7 +8716,7 @@ void __init kmem_cache_init(void)
 
 	pr_info("SLUB: HWalign=%d, Order=%u-%u, MinObjects=%u, CPUs=%u, Nodes=%u\n",
 		cache_line_size(),
-		slub_min_order, slub_max_order, slub_min_objects,
+		slab_min_order, slab_max_order, slab_min_objects,
 		nr_cpu_ids, nr_node_ids);
 }
 

-- 
2.55.0