Unify /proc/slabinfo configuration

Both SLUB and SLAB really did almost exactly the same thing for
/proc/slabinfo setup, using duplicate code and per-allocator #ifdef's.

This just creates a common CONFIG_SLABINFO that is enabled by both SLUB
and SLAB, and shares all the setup code.  Maybe SLOB will want this some
day too.

Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/slab.h b/include/linux/slab.h
index f3a8eec..f62caaa 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -271,5 +271,10 @@
 	return kmalloc(size, flags | __GFP_ZERO);
 }
 
+#ifdef CONFIG_SLABINFO
+extern const struct seq_operations slabinfo_op;
+ssize_t slabinfo_write(struct file *, const char __user *, size_t, loff_t *);
+#endif
+
 #endif	/* __KERNEL__ */
 #endif	/* _LINUX_SLAB_H */