cgroup/cpuset: use hotplug_memory_notifier() directly

Patch series "mm: Use hotplug_memory_notifier() instead of
register_hotmemory_notifier()", v4.

Commit f02c6968 ("include/linux/memory.h: implement
register_hotmemory_notifier()") introduced register_hotmemory_notifier()
to avoid a compile problem with gcc-4.4.4:

    When CONFIG_MEMORY_HOTPLUG=n, we don't want the memory-hotplug notifier
    handlers to be included in the .o files, for space reasons.
    
    The existing hotplug_memory_notifier() tries to handle this but testing
    with gcc-4.4.4 shows that it doesn't work - the hotplug functions are
    still present in the .o files.

Since commit 76ae8474 ("Documentation: raise minimum supported
version of GCC to 5.1") has already updated the minimum gcc version to
5.1.  The previous problem mentioned in f02c6968 does not exist.  So
we can now revert to use hotplug_memory_notifier() directly rather than
register_hotmemory_notifier().

In the last patch, we move all hotplug memory notifier priority to same
file for easy sorting.


This patch (of 8):

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/20220923033347.3935160-1-liushixin2@huawei.com
Link: https://lkml.kernel.org/r/20220923033347.3935160-2-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>

kernel/cgroup/cpuset.c

@@ -3630,11 +3630,6 @@ static int cpuset_track_online_nodes(struct notifier_block *self,
 	return NOTIFY_OK;
 }
 
-static struct notifier_block cpuset_track_online_nodes_nb = {
-	.notifier_call = cpuset_track_online_nodes,
-	.priority = 10,		/* ??! */
-};
-
 /**
  * cpuset_init_smp - initialize cpus_allowed
  *
@@ -3652,7 +3647,7 @@ void __init cpuset_init_smp(void)
 	cpumask_copy(top_cpuset.effective_cpus, cpu_active_mask);
 	top_cpuset.effective_mems = node_states[N_MEMORY];
 
-	register_hotmemory_notifier(&cpuset_track_online_nodes_nb);
+	hotplug_memory_notifier(cpuset_track_online_nodes, 10);
 
 	cpuset_migrate_mm_wq = alloc_ordered_workqueue("cpuset_migrate_mm", 0);
 	BUG_ON(!cpuset_migrate_mm_wq);