slub: make ->reserved unsigned int

->reserved is either 0 or sizeof(struct rcu_head), can't be negative.

Link: http://lkml.kernel.org/r/20180305200730.15812-12-adobriyan@gmail.com
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/slub_def.h

@@ -100,7 +100,7 @@ struct kmem_cache {
 	void (*ctor)(void *);
 	int inuse;		/* Offset to metadata */
 	int align;		/* Alignment */
-	int reserved;		/* Reserved bytes at the end of slabs */
+	unsigned int reserved;		/* Reserved bytes at the end of slabs */
 	unsigned int red_left_pad;	/* Left redzone padding size */
 	const char *name;	/* Name (only for display!) */
 	struct list_head list;	/* List of slab caches */

mm/slub.c

@@ -5094,7 +5094,7 @@ SLAB_ATTR_RO(destroy_by_rcu);
 
 static ssize_t reserved_show(struct kmem_cache *s, char *buf)
 {
-	return sprintf(buf, "%d\n", s->reserved);
+	return sprintf(buf, "%u\n", s->reserved);
 }
 SLAB_ATTR_RO(reserved);