mm, sl[aou]b: Extract common fields from struct kmem_cache

Define a struct that describes common fields used in all slab allocators.
A slab allocator either uses the common definition (like SLOB) or is
required to provide members of kmem_cache with the definition given.

After that it will be possible to share code that
only operates on those fields of kmem_cache.

The patch basically takes the slob definition of kmem cache and
uses the field namees for the other allocators.

It also standardizes the names used for basic object lengths in
allocators:

object_size	Struct size specified at kmem_cache_create. Basically
		the payload expected to be used by the subsystem.

size		The size of memory allocator for each object. This size
		is larger than object_size and includes padding, alignment
		and extra metadata for each object (f.e. for debugging
		and rcu).
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

include/linux/slab.h

@@ -92,6 +92,30 @@
 #define ZERO_OR_NULL_PTR(x) ((unsigned long)(x) <= \
 				(unsigned long)ZERO_SIZE_PTR)
 
+/*
+ * Common fields provided in kmem_cache by all slab allocators
+ * This struct is either used directly by the allocator (SLOB)
+ * or the allocator must include definitions for all fields
+ * provided in kmem_cache_common in their definition of kmem_cache.
+ *
+ * Once we can do anonymous structs (C11 standard) we could put a
+ * anonymous struct definition in these allocators so that the
+ * separate allocations in the kmem_cache structure of SLAB and
+ * SLUB is no longer needed.
+ */
+#ifdef CONFIG_SLOB
+struct kmem_cache {
+	unsigned int object_size;/* The original size of the object */
+	unsigned int size;	/* The aligned/padded/added on size  */
+	unsigned int align;	/* Alignment as calculated */
+	unsigned long flags;	/* Active flags on the slab */
+	const char *name;	/* Slab name for sysfs */
+	int refcount;		/* Use counter */
+	void (*ctor)(void *);	/* Called on object slot creation */
+	struct list_head list;	/* List of all slab caches on the system */
+};
+#endif
+
 /*
  * struct kmem_cache related prototypes
  */

include/linux/slab_def.h

@@ -27,7 +27,7 @@ struct kmem_cache {
 	unsigned int limit;
 	unsigned int shared;
 
-	unsigned int buffer_size;
+	unsigned int size;
 	u32 reciprocal_buffer_size;
 /* 2) touched by every alloc & free from the backend */
 
@@ -52,7 +52,10 @@ struct kmem_cache {
 
 /* 4) cache creation/removal */
 	const char *name;
-	struct list_head next;
+	struct list_head list;
+	int refcount;
+	int object_size;
+	int align;
 
 /* 5) statistics */
 #ifdef CONFIG_DEBUG_SLAB
@@ -73,12 +76,11 @@ struct kmem_cache {
 
 	/*
 	 * If debugging is enabled, then the allocator can add additional
-	 * fields and/or padding to every object. buffer_size contains the total
+	 * fields and/or padding to every object. size contains the total
 	 * object size including these internal fields, the following two
 	 * variables contain the offset to the user object and its size.
 	 */
 	int obj_offset;
-	int obj_size;
 #endif /* CONFIG_DEBUG_SLAB */
 
 /* 6) per-cpu/per-node data, touched during every alloc/free */

include/linux/slub_def.h

@@ -82,7 +82,7 @@ struct kmem_cache {
 	unsigned long flags;
 	unsigned long min_partial;
 	int size;		/* The size of an object including meta data */
-	int objsize;		/* The size of an object without meta data */
+	int object_size;	/* The size of an object without meta data */
 	int offset;		/* Free pointer offset. */
 	int cpu_partial;	/* Number of per cpu partial objects to keep around */
 	struct kmem_cache_order_objects oo;

mm/slob.c

@@ -506,13 +506,6 @@ size_t ksize(const void *block)
 }
 EXPORT_SYMBOL(ksize);
 
-struct kmem_cache {
-	unsigned int size, align;
-	unsigned long flags;
-	const char *name;
-	void (*ctor)(void *);
-};
-
 struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 	size_t align, unsigned long flags, void (*ctor)(void *))
 {
@@ -523,7 +516,7 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 
 	if (c) {
 		c->name = name;
-		c->size = size;
+		c->size = c->object_size;
 		if (flags & SLAB_DESTROY_BY_RCU) {
 			/* leave room for rcu footer at the end of object */
 			c->size += sizeof(struct slob_rcu);