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Subject[PATCH v15 06/10] mm/demotion: Add pg_data_t member to track node memory tier details
Date
Also update different helpes to use NODE_DATA()->memtier. Since
node specific memtier can change based on the reassignment of
NUMA node to a different memory tiers, accessing NODE_DATA()->memtier
needs to happen under an rcu read lock or memory_tier_lock.

Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
include/linux/mmzone.h | 3 +++
mm/memory-tiers.c | 40 +++++++++++++++++++++++++++++++++++-----
2 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index e24b40c52468..7d78133fe8dd 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1012,6 +1012,9 @@ typedef struct pglist_data {
/* Per-node vmstats */
struct per_cpu_nodestat __percpu *per_cpu_nodestats;
atomic_long_t vm_stat[NR_VM_NODE_STAT_ITEMS];
+#ifdef CONFIG_NUMA
+ struct memory_tier __rcu *memtier;
+#endif
} pg_data_t;

#define node_present_pages(nid) (NODE_DATA(nid)->node_present_pages)
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index c29bb24449b8..2b7e91b45a75 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -4,6 +4,7 @@
#include <linux/sysfs.h>
#include <linux/kobject.h>
#include <linux/memory.h>
+#include <linux/mmzone.h>
#include <linux/memory-tiers.h>

#include "internal.h"
@@ -136,12 +137,18 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty

static struct memory_tier *__node_get_memory_tier(int node)
{
- struct memory_dev_type *memtype;
+ pg_data_t *pgdat;

- memtype = node_memory_types[node];
- if (memtype && node_isset(node, memtype->nodes))
- return memtype->memtier;
- return NULL;
+ pgdat = NODE_DATA(node);
+ if (!pgdat)
+ return NULL;
+ /*
+ * Since we hold memory_tier_lock, we can avoid
+ * RCU read locks when accessing the details. No
+ * parallel updates are possible here.
+ */
+ return rcu_dereference_check(pgdat->memtier,
+ lockdep_is_held(&memory_tier_lock));
}

#ifdef CONFIG_MIGRATION
@@ -294,6 +301,8 @@ static struct memory_tier *set_node_memory_tier(int node)
{
struct memory_tier *memtier;
struct memory_dev_type *memtype;
+ pg_data_t *pgdat = NODE_DATA(node);
+

lockdep_assert_held_once(&memory_tier_lock);

@@ -305,24 +314,45 @@ static struct memory_tier *set_node_memory_tier(int node)
memtype = node_memory_types[node];
node_set(node, memtype->nodes);
memtier = find_create_memory_tier(memtype);
+ if (!IS_ERR(memtier))
+ rcu_assign_pointer(pgdat->memtier, memtier);
return memtier;
}

static void destroy_memory_tier(struct memory_tier *memtier)
{
list_del(&memtier->list);
+ /*
+ * synchronize_rcu in clear_node_memory_tier makes sure
+ * we don't have rcu access to this memory tier.
+ */
kfree(memtier);
}

static bool clear_node_memory_tier(int node)
{
bool cleared = false;
+ pg_data_t *pgdat;
struct memory_tier *memtier;

+ pgdat = NODE_DATA(node);
+ if (!pgdat)
+ return false;
+
+ /*
+ * Make sure that anybody looking at NODE_DATA who finds
+ * a valid memtier finds memory_dev_types with nodes still
+ * linked to the memtier. We achieve this by waiting for
+ * rcu read section to finish using synchronize_rcu.
+ * This also enables us to free the destroyed memory tier
+ * with kfree instead of kfree_rcu
+ */
memtier = __node_get_memory_tier(node);
if (memtier) {
struct memory_dev_type *memtype;

+ rcu_assign_pointer(pgdat->memtier, NULL);
+ synchronize_rcu();
memtype = node_memory_types[node];
node_clear(node, memtype->nodes);
if (nodes_empty(memtype->nodes)) {
--
2.37.2
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