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>

1 files changed, 24 insertions, 0 deletions

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 67d5d94..0dd2dfa 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -93,6 +93,30 @@
 				(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
  */
 void __init kmem_cache_init(void);