mm/slub.c: use hotplug_memory_notifier() directly

Commit 76ae8474 ("Documentation: raise minimum supported version of
GCC to 5.1") updated the minimum gcc version to 5.1.  So the problem
mentioned in f02c6968 ("include/linux/memory.h: implement
register_hotmemory_notifier()") no longer exist.  So we can now switch to
use hotplug_memory_notifier() directly rather than
register_hotmemory_notifier().

Link: https://lkml.kernel.org/r/20220923033347.3935160-4-liushixin2@huawei.comSigned-off-by: Liu Shixin <liushixin2@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Waiman Long <longman@redhat.com>
Cc: zefan li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/slub.c

@@ -4771,11 +4771,6 @@ static int slab_memory_callback(struct notifier_block *self,
 	return ret;
 }
 
-static struct notifier_block slab_memory_callback_nb = {
-	.notifier_call = slab_memory_callback,
-	.priority = SLAB_CALLBACK_PRI,
-};
-
 /********************************************************************
  *			Basic setup of slabs
  *******************************************************************/
@@ -4841,7 +4836,7 @@ void __init kmem_cache_init(void)
 	create_boot_cache(kmem_cache_node, "kmem_cache_node",
 		sizeof(struct kmem_cache_node), SLAB_HWCACHE_ALIGN, 0, 0);
 
-	register_hotmemory_notifier(&slab_memory_callback_nb);
+	hotplug_memory_notifier(slab_memory_callback, SLAB_CALLBACK_PRI);
 
 	/* Able to allocate the per node structures */
 	slab_state = PARTIAL;