[PATCH -mm 1/6] slab: introduce __kfree_rcu

[Lai Jiangshan <laijs@cn.fujitsu.com>]

Introduce __kfree_rcu() for kfree_rcu()

We can calculate the object poiter from a poiter inside this
object in slab.c, so we can use a portion_to_obj() to instead
various container_of() for rcu callback and free the object.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/mm/slab.c b/mm/slab.c
index 4d00855..a067d3f 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -634,6 +634,17 @@ static inline unsigned int obj_to_index(const struct kmem_cache *cache,
 	return reciprocal_divide(offset, cache->reciprocal_buffer_size);
 }
 
+static inline void *portion_to_obj(void *portion)
+{
+	struct page *page = virt_to_head_page(portion);
+	struct slab *slab = page_get_slab(page);
+	struct kmem_cache *cache = page_get_cache(page);
+	unsigned int offset = portion - slab->s_mem;
+	unsigned int index = offset / cache->buffer_size;
+
+	return index_to_obj(cache, slab, index);
+}
+
 /*
  * These are the default caches for kmalloc. Custom caches can have other sizes.
  */
@@ -3728,6 +3739,17 @@ void kfree(const void *objp)
 }
 EXPORT_SYMBOL(kfree);
 
+static void kfree_rcu_callback(struct rcu_head *rcu)
+{
+	kfree(portion_to_obj(rcu));
+}
+
+void __kfree_rcu(const void *objp, struct rcu_head *rcu)
+{
+	call_rcu(rcu, kfree_rcu_callback);
+}
+EXPORT_SYMBOL(__kfree_rcu);
+
 unsigned int kmem_cache_size(struct kmem_cache *cachep)
 {
 	return obj_size(cachep);