mm/memory_hotplug.c: simplify node_states_check_changes_online

While looking at node_states_check_changes_online, I stumbled upon some
confusing things.

Right after entering the function, we find this:

if (N_MEMORY == N_NORMAL_MEMORY)
        zone_last = ZONE_MOVABLE;

This is wrong.
N_MEMORY cannot really be equal to N_NORMAL_MEMORY.
My guess is that this wanted to be something like:

if (N_NORMAL_MEMORY == N_HIGH_MEMORY)

to check if we have CONFIG_HIGHMEM.

Later on, in the CONFIG_HIGHMEM block, we have:

if (N_MEMORY == N_HIGH_MEMORY)
        zone_last = ZONE_MOVABLE;

Again, this is wrong, and will never be evaluated to true.

Besides removing these wrong if statements, I simplified the function a
bit.

[osalvador@suse.de: address feedback from Pavel]
  Link: http://lkml.kernel.org/r/20180921132634.10103-4-osalvador@techadventures.net
Link: http://lkml.kernel.org/r/20180919100819.25518-5-osalvador@techadventures.net
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Pavel Tatashin <pavel.tatashin@microsoft.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Mathieu Malaterre <malat@debian.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: <yasu.isimatu@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 50 deletions

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 561c44761f95..eadd149eb7bc 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -687,62 +687,19 @@ static void node_states_check_changes_online(unsigned long nr_pages,
         struct zone *zone, struct memory_notify *arg)
 {
         int nid = zone_to_nid(zone);
-        enum zone_type zone_last = ZONE_NORMAL;
 
-        /*
-         * If we have HIGHMEM or movable node, node_states[N_NORMAL_MEMORY]
-         * contains nodes which have zones of 0...ZONE_NORMAL,
-         * set zone_last to ZONE_NORMAL.
-         *
-         * If we don't have HIGHMEM nor movable node,
-         * node_states[N_NORMAL_MEMORY] contains nodes which have zones of
-         * 0...ZONE_MOVABLE, set zone_last to ZONE_MOVABLE.
-         */
-        if (N_MEMORY == N_NORMAL_MEMORY)
-                zone_last = ZONE_MOVABLE;
+        arg->status_change_nid = -1;
+        arg->status_change_nid_normal = -1;
+        arg->status_change_nid_high = -1;
 
-        /*
-         * if the memory to be online is in a zone of 0...zone_last, and
-         * the zones of 0...zone_last don't have memory before online, we will
-         * need to set the node to node_states[N_NORMAL_MEMORY] after
-         * the memory is online.
-         */
-        if (zone_idx(zone) <= zone_last && !node_state(nid, N_NORMAL_MEMORY))
+        if (!node_state(nid, N_MEMORY))
+                arg->status_change_nid = nid;
+        if (zone_idx(zone) <= ZONE_NORMAL && !node_state(nid, N_NORMAL_MEMORY))
                 arg->status_change_nid_normal = nid;
-        else
-                arg->status_change_nid_normal = -1;
-
 #ifdef CONFIG_HIGHMEM
-        /*
-         * If we have movable node, node_states[N_HIGH_MEMORY]
-         * contains nodes which have zones of 0...ZONE_HIGHMEM,
-         * set zone_last to ZONE_HIGHMEM.
-         *
-         * If we don't have movable node, node_states[N_NORMAL_MEMORY]
-         * contains nodes which have zones of 0...ZONE_MOVABLE,
-         * set zone_last to ZONE_MOVABLE.
-         */
-        zone_last = ZONE_HIGHMEM;
-        if (N_MEMORY == N_HIGH_MEMORY)
-                zone_last = ZONE_MOVABLE;
-
-        if (zone_idx(zone) <= zone_last && !node_state(nid, N_HIGH_MEMORY))
+        if (zone_idx(zone) <= N_HIGH_MEMORY && !node_state(nid, N_HIGH_MEMORY))
                 arg->status_change_nid_high = nid;
-        else
-                arg->status_change_nid_high = -1;
-#else
-        arg->status_change_nid_high = arg->status_change_nid_normal;
 #endif
-
-        /*
-         * if the node don't have memory befor online, we will need to
-         * set the node to node_states[N_MEMORY] after the memory
-         * is online.
-         */
-        if (!node_state(nid, N_MEMORY))
-                arg->status_change_nid = nid;
-        else
-                arg->status_change_nid = -1;
 }
 
 static void node_states_set_node(int node, struct memory_notify *arg)