ipc: define the slab_memory_callback priority as a constant

This is a trivial patch that defines the priority of slab_memory_callback in
the callback chain as a constant. This is to prepare for next patch in the
series.

Signed-off-by: Nadia Derbey <[e-mail]>
Cc: Yasunori Goto <[e-mail]>
Cc: Matt Helsley <[e-mail]>
Cc: Mingming Cao <[e-mail]>
Cc: Pierre Peiffer <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/memory.h

···
 struct notifier_block;
 struct mem_section;
 
+/*
+ * Priorities for the hotplug memory callback routines (stored in decreasing
+ * order in the callback chain)
+ */
+#define SLAB_CALLBACK_PRI       1
+
 #ifndef CONFIG_MEMORY_HOTPLUG_SPARSE
 static inline int memory_dev_init(void)
 {

mm/slub.c

···
 	kmalloc_caches[0].refcount = -1;
 	caches++;
 
-	hotplug_memory_notifier(slab_memory_callback, 1);
+	hotplug_memory_notifier(slab_memory_callback, SLAB_CALLBACK_PRI);
 #endif
 
 	/* Able to allocate the per node structures */