Explain kmem_cache_cpu fields

Add some comments explaining the fields of the kmem_cache_cpu structure.

Signed-off-by: Christoph Lameter <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/slub_def.h

···
 #include <linux/kobject.h>
 
 struct kmem_cache_cpu {
-	void **freelist;
-	struct page *page;
-	int node;
-	unsigned int offset;
-	unsigned int objsize;
+	void **freelist;	/* Pointer to first free per cpu object */
+	struct page *page;	/* The slab from which we are allocating */
+	int node;		/* The node of the page (or -1 for debug) */
+	unsigned int offset;	/* Freepointer offset (in word units) */
+	unsigned int objsize;	/* Size of an object (from kmem_cache) */
 };
 
 struct kmem_cache_node {