2 files changed, 31 insertions, 17 deletions

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 8b6e8ae5d5ca..ae0093cc5189 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -83,6 +83,7 @@ struct kmem_cache {
         void (*ctor)(void *);
         int inuse;              /* Offset to metadata */
         int align;              /* Alignment */
+        int reserved;           /* Reserved bytes at the end of slabs */
         unsigned long min_partial;
         const char *name;       /* Name (only for display!) */
         struct list_head list;  /* List of slab caches */
diff --git a/mm/slub.c b/mm/slub.c
index e15aa7f193c9..d3d17677bab5 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -281,11 +281,16 @@ static inline int slab_index(void *p, struct kmem_cache *s, void *addr)
         return (p - addr) / s->size;
 }
 
+static inline int order_objects(int order, unsigned long size, int reserved)
+{
+        return ((PAGE_SIZE << order) - reserved) / size;
+}
+
 static inline struct kmem_cache_order_objects oo_make(int order,
-                                                unsigned long size)
+                unsigned long size, int reserved)
 {
         struct kmem_cache_order_objects x = {
-                (order << OO_SHIFT) + (PAGE_SIZE << order) / size
+                (order << OO_SHIFT) + order_objects(order, size, reserved)
         };
 
         return x;
@@ -617,7 +622,7 @@ static int slab_pad_check(struct kmem_cache *s, struct page *page)
                 return 1;
 
         start = page_address(page);
-        length = (PAGE_SIZE << compound_order(page));
+        length = (PAGE_SIZE << compound_order(page)) - s->reserved;
         end = start + length;
         remainder = length % s->size;
         if (!remainder)
@@ -698,7 +703,7 @@ static int check_slab(struct kmem_cache *s, struct page *page)
                 return 0;
         }
 
-        maxobj = (PAGE_SIZE << compound_order(page)) / s->size;
+        maxobj = order_objects(compound_order(page), s->size, s->reserved);
         if (page->objects > maxobj) {
                 slab_err(s, page, "objects %u > max %u",
                         s->name, page->objects, maxobj);
@@ -748,7 +753,7 @@ static int on_freelist(struct kmem_cache *s, struct page *page, void *search)
                 nr++;
         }
 
-        max_objects = (PAGE_SIZE << compound_order(page)) / s->size;
+        max_objects = order_objects(compound_order(page), s->size, s->reserved);
         if (max_objects > MAX_OBJS_PER_PAGE)
                 max_objects = MAX_OBJS_PER_PAGE;
 
@@ -1988,13 +1993,13 @@ static int slub_nomerge;
  * the smallest order which will fit the object.
  */
 static inline int slab_order(int size, int min_objects,
-                                int max_order, int fract_leftover)
+                                int max_order, int fract_leftover, int reserved)
 {
         int order;
         int rem;
         int min_order = slub_min_order;
 
-        if ((PAGE_SIZE << min_order) / size > MAX_OBJS_PER_PAGE)
+        if (order_objects(min_order, size, reserved) > MAX_OBJS_PER_PAGE)
                 return get_order(size * MAX_OBJS_PER_PAGE) - 1;
 
         for (order = max(min_order,
@@ -2003,10 +2008,10 @@ static inline int slab_order(int size, int min_objects,
 
                 unsigned long slab_size = PAGE_SIZE << order;
 
-                if (slab_size < min_objects * size)
+                if (slab_size < min_objects * size + reserved)
                         continue;
 
-                rem = slab_size % size;
+                rem = (slab_size - reserved) % size;
 
                 if (rem <= slab_size / fract_leftover)
                         break;
@@ -2016,7 +2021,7 @@ static inline int slab_order(int size, int min_objects,
         return order;
 }
 
-static inline int calculate_order(int size)
+static inline int calculate_order(int size, int reserved)
 {
         int order;
         int min_objects;
@@ -2034,14 +2039,14 @@ static inline int calculate_order(int size)
         min_objects = slub_min_objects;
         if (!min_objects)
                 min_objects = 4 * (fls(nr_cpu_ids) + 1);
-        max_objects = (PAGE_SIZE << slub_max_order)/size;
+        max_objects = order_objects(slub_max_order, size, reserved);
         min_objects = min(min_objects, max_objects);
 
         while (min_objects > 1) {
                 fraction = 16;
                 while (fraction >= 4) {
                         order = slab_order(size, min_objects,
-                                                slub_max_order, fraction);
+                                        slub_max_order, fraction, reserved);
                         if (order <= slub_max_order)
                                 return order;
                         fraction /= 2;
@@ -2053,14 +2058,14 @@ static inline int calculate_order(int size)
          * We were unable to place multiple objects in a slab. Now
          * lets see if we can place a single object there.
          */
-        order = slab_order(size, 1, slub_max_order, 1);
+        order = slab_order(size, 1, slub_max_order, 1, reserved);
         if (order <= slub_max_order)
                 return order;
 
         /*
          * Doh this slab cannot be placed using slub_max_order.
          */
-        order = slab_order(size, 1, MAX_ORDER, 1);
+        order = slab_order(size, 1, MAX_ORDER, 1, reserved);
         if (order < MAX_ORDER)
                 return order;
         return -ENOSYS;
@@ -2311,7 +2316,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
         if (forced_order >= 0)
                 order = forced_order;
         else
-                order = calculate_order(size);
+                order = calculate_order(size, s->reserved);
 
         if (order < 0)
                 return 0;
@@ -2329,8 +2334,8 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
         /*
          * Determine the number of objects per slab
          */
-        s->oo = oo_make(order, size);
-        s->min = oo_make(get_order(size), size);
+        s->oo = oo_make(order, size, s->reserved);
+        s->min = oo_make(get_order(size), size, s->reserved);
         if (oo_objects(s->oo) > oo_objects(s->max))
                 s->max = s->oo;
 
@@ -2349,6 +2354,7 @@ static int kmem_cache_open(struct kmem_cache *s,
         s->objsize = size;
         s->align = align;
         s->flags = kmem_cache_flags(size, flags, name, ctor);
+        s->reserved = 0;
 
         if (!calculate_sizes(s, -1))
                 goto error;
@@ -4017,6 +4023,12 @@ static ssize_t destroy_by_rcu_show(struct kmem_cache *s, char *buf)
 }
 SLAB_ATTR_RO(destroy_by_rcu);
 
+static ssize_t reserved_show(struct kmem_cache *s, char *buf)
+{
+        return sprintf(buf, "%d\n", s->reserved);
+}
+SLAB_ATTR_RO(reserved);
+
 #ifdef CONFIG_SLUB_DEBUG
 static ssize_t slabs_show(struct kmem_cache *s, char *buf)
 {
@@ -4303,6 +4315,7 @@ static struct attribute *slab_attrs[] = {
         &reclaim_account_attr.attr,
         &destroy_by_rcu_attr.attr,
         &shrink_attr.attr,
+        &reserved_attr.attr,
 #ifdef CONFIG_SLUB_DEBUG
         &total_objects_attr.attr,
         &slabs_attr.attr,