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Subject[PATCH 4/5] mm/memory_hotplug: Simplify node_states_check_changes_online
Date
From: Oscar Salvador <osalvador@suse.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@suse.de>
---
mm/memory_hotplug.c | 71 +++++++++++++++++------------------------------------
1 file changed, 23 insertions(+), 48 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 131c08106d54..ab3c1de18c5d 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -687,61 +687,36 @@ 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.
+ * zone_for_pfn_range() can only return a zone within
+ * (0..ZONE_NORMAL] or ZONE_MOVABLE.
+ * If the zone is within the range (0..ZONE_NORMAL],
+ * we need to check if:
+ * 1) We need to set the node for N_NORMAL_MEMORY
+ * 2) On CONFIG_HIGHMEM systems, we need to also set
+ * the node for N_HIGH_MEMORY.
+ * 3) On !CONFIG_HIGHMEM, we can disregard N_HIGH_MEMORY,
+ * as N_HIGH_MEMORY falls back to N_NORMAL_MEMORY.
*/
- if (N_MEMORY == N_NORMAL_MEMORY)
- zone_last = ZONE_MOVABLE;

- /*
- * 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))
- 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_NORMAL) {
+ if (!node_state(nid, N_NORMAL_MEMORY))
+ arg->status_change_nid_normal = nid;
+ else
+ arg->status_change_nid_normal = -1;

- if (zone_idx(zone) <= zone_last && !node_state(nid, N_HIGH_MEMORY))
- arg->status_change_nid_high = nid;
- else
- arg->status_change_nid_high = -1;
-#else
- /*
- * When !CONFIG_HIGHMEM, N_HIGH_MEMORY equals N_NORMAL_MEMORY
- * so setting the node for N_NORMAL_MEMORY is enough.
- */
- arg->status_change_nid_high = -1;
-#endif
+ if (IS_ENABLED(CONFIG_HIGHMEM)) {
+ if (!node_state(nid, N_HIGH_MEMORY))
+ arg->status_change_nid_high = nid;
+ } else
+ arg->status_change_nid_high = -1;
+ }

/*
- * 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 the node doesn't have memory before onlining it, we will need
+ * to set the node to node_states[N_MEMORY] after the memory
+ * gets onlined.
*/
if (!node_state(nid, N_MEMORY))
arg->status_change_nid = nid;
--
2.13.6
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