linux-kernel - [PATCH v2 3/4] mm/memory_hotplug: Simplify node_states_check_changes

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Date:   Fri, 21 Sep 2018 15:26:33 +0200
From:   Oscar Salvador <osalvador@...hadventures.net>
To:     akpm@...ux-foundation.org
Cc:     mhocko@...e.com, dan.j.williams@...el.com, david@...hat.com,
        Pavel.Tatashin@...rosoft.com, Jonathan.Cameron@...wei.com,
        yasu.isimatu@...il.com, malat@...ian.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Oscar Salvador <osalvador@...e.de>
Subject: [PATCH v2 3/4] mm/memory_hotplug: Simplify node_states_check_changes_online

From: Oscar Salvador <osalvador@...e.de>

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.

Signed-off-by: Oscar Salvador <osalvador@...e.de>
Suggested-by: Pavel Tatashin <pavel.tatashin@...rosoft.com>
---
 mm/memory_hotplug.c | 57 +++++++----------------------------------------------
 1 file 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)
-- 
2.13.6