[PATCH mm-unstable] mm/demotion: Assign correct memory type for multiple dax devices with the same node affinity

From: Aneesh Kumar K.V
Date: Fri Aug 26 2022 - 06:05:45 EST


With multiple dax devices having the same node affinity, the kernel wrongly assigned
default_dram memory type to some devices after the memory hotplug operation. Fix this by
not clearing node_memory_types on the dax device remove.

The current kernel cleared node_memory_type on successful removal of a dax device.
But then we can have multiple dax devices with the same node affinity. Clearing the
node_memory_type results in assigning other dax devices to the default dram type when
we bring them online.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
---
mm/memory-tiers.c | 37 +++++++++++++++++++++++++++++--------
1 file changed, 29 insertions(+), 8 deletions(-)

diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index ba844fe9cc8c..c4bd6d052a33 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -27,9 +27,14 @@ struct demotion_nodes {
nodemask_t preferred;
};

+struct node_memory_type_map {
+ struct memory_dev_type *memtype;
+ int map_count;
+};
+
static DEFINE_MUTEX(memory_tier_lock);
static LIST_HEAD(memory_tiers);
-static struct memory_dev_type *node_memory_types[MAX_NUMNODES];
+static struct node_memory_type_map node_memory_types[MAX_NUMNODES];
static struct memory_dev_type *default_dram_type;
#ifdef CONFIG_MIGRATION
static int top_tier_adistance;
@@ -386,9 +391,19 @@ static inline void establish_demotion_targets(void) {}

static inline void __init_node_memory_type(int node, struct memory_dev_type *memtype)
{
- if (!node_memory_types[node]) {
- node_memory_types[node] = memtype;
- kref_get(&memtype->kref);
+ if (!node_memory_types[node].memtype)
+ node_memory_types[node].memtype = memtype;
+ /*
+ * for each device getting added in the same NUMA node
+ * with this specific memtype, bump the map count. We
+ * Only take memtype device reference once, so that
+ * changing a node memtype can be done by droping the
+ * only reference count taken here.
+ */
+
+ if (node_memory_types[node].memtype == memtype) {
+ if (!node_memory_types[node].map_count++)
+ kref_get(&memtype->kref);
}
}

@@ -406,7 +421,7 @@ static struct memory_tier *set_node_memory_tier(int node)

__init_node_memory_type(node, default_dram_type);

- memtype = node_memory_types[node];
+ memtype = node_memory_types[node].memtype;
node_set(node, memtype->nodes);
memtier = find_create_memory_tier(memtype);
if (!IS_ERR(memtier))
@@ -448,7 +463,7 @@ static bool clear_node_memory_tier(int node)

rcu_assign_pointer(pgdat->memtier, NULL);
synchronize_rcu();
- memtype = node_memory_types[node];
+ memtype = node_memory_types[node].memtype;
node_clear(node, memtype->nodes);
if (nodes_empty(memtype->nodes)) {
list_del_init(&memtype->tier_sibiling);
@@ -502,8 +517,14 @@ EXPORT_SYMBOL_GPL(init_node_memory_type);
void clear_node_memory_type(int node, struct memory_dev_type *memtype)
{
mutex_lock(&memory_tier_lock);
- if (node_memory_types[node] == memtype) {
- node_memory_types[node] = NULL;
+ if (node_memory_types[node].memtype == memtype)
+ node_memory_types[node].map_count--;
+ /*
+ * If we umapped all the attached devices to this node,
+ * clear the node memory type.
+ */
+ if (!node_memory_types[node].map_count) {
+ node_memory_types[node].memtype = NULL;
kref_put(&memtype->kref, release_memtype);
}
mutex_unlock(&memory_tier_lock);
--
2.37.2