mm/slub: refactor calculate_order() and calc_slab_order()

After the previous cleanups, we can now move some code from
calc_slab_order() to calculate_order() so it's executed just once, and
do some more cleanups.

- move the min_order and MAX_OBJS_PER_PAGE evaluation to
  calculate_order().

- change calc_slab_order() parameter min_objects to min_order

Also make MAX_OBJS_PER_PAGE check more robust by considering also
min_objects in addition to slub_min_order. Otherwise this is not a
functional change.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Feng Tang <feng.tang@intel.com>
Reviewed-and-tested-by: Jay Patel <jaypatel@linux.ibm.com>

diff --git a/mm/slub.c b/mm/slub.c
index 86141e5164ca088eda0154313a56a85606e55e47..63d281dfacdbca13ff951a4dcacc031d1b6536c0 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4110,17 +4110,12 @@ static unsigned int slub_min_objects;
  * the smallest order which will fit the object.
  */
 static inline unsigned int calc_slab_order(unsigned int size,
-               unsigned int min_objects, unsigned int max_order,
+               unsigned int min_order, unsigned int max_order,
                unsigned int fract_leftover)
 {
-       unsigned int min_order = slub_min_order;
        unsigned int order;
 
-       if (order_objects(min_order, size) > MAX_OBJS_PER_PAGE)
-               return get_order(size * MAX_OBJS_PER_PAGE) - 1;
-
-       for (order = max(min_order, (unsigned int)get_order(min_objects * size));
-                       order <= max_order; order++) {
+       for (order = min_order; order <= max_order; order++) {
 
                unsigned int slab_size = (unsigned int)PAGE_SIZE << order;
                unsigned int rem;
@@ -4139,7 +4134,7 @@ static inline int calculate_order(unsigned int size)
        unsigned int order;
        unsigned int min_objects;
        unsigned int max_objects;
-       unsigned int nr_cpus;
+       unsigned int min_order;
 
        min_objects = slub_min_objects;
        if (!min_objects) {
@@ -4152,14 +4147,20 @@ static inline int calculate_order(unsigned int size)
                 * order on systems that appear larger than they are, and too
                 * low order on systems that appear smaller than they are.
                 */
-               nr_cpus = num_present_cpus();
+               unsigned int nr_cpus = num_present_cpus();
                if (nr_cpus <= 1)
                        nr_cpus = nr_cpu_ids;
                min_objects = 4 * (fls(nr_cpus) + 1);
        }
-       max_objects = order_objects(slub_max_order, size);
+       /* min_objects can't be 0 because get_order(0) is undefined */
+       max_objects = max(order_objects(slub_max_order, size), 1U);
        min_objects = min(min_objects, max_objects);
 
+       min_order = max_t(unsigned int, slub_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;
+
        /*
         * Attempt to find best configuration for a slab. This works by first
         * attempting to generate a layout with the best possible configuration
@@ -4176,7 +4177,7 @@ static inline int calculate_order(unsigned int size)
         * long as at least single object fits within slub_max_order.
         */
        for (unsigned int fraction = 16; fraction > 1; fraction /= 2) {
-               order = calc_slab_order(size, min_objects, slub_max_order,
+               order = calc_slab_order(size, min_order, slub_max_order,
                                        fraction);
                if (order <= slub_max_order)
                        return order;