[PATCH v2 1/1] memory tier: consolidate the initialization of memory tiers

["Ho-Ren (Jack) Chuang" <horen.chuang@linux.dev>]

If we simply move the set_node_memory_tier() from memory_tier_init()
to late_initcall(), it will result in HMAT not registering
the mt_adistance_algorithm callback function, because
set_node_memory_tier() is not performed during the memory tiering
initialization phase, leading to a lack of correct default_dram
information.

Therefore, we introduced a nodemask to pass the information of the
default DRAM nodes. The reason for not choosing to reuse
default_dram_type->nodes is that it is not clean enough. So in the end,
we use a __initdata variable, which is a variable that is released once
initialization is complete, including both CPU and memory nodes for HMAT
to iterate through.

Besides, since default_dram_type may be checked/used during the
initialization process of HMAT and drivers, it is better to keep the
allocation of default_dram_type in memory_tier_init().

Signed-off-by: Ho-Ren (Jack) Chuang <horenchuang@bytedance.com>
Suggested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 drivers/acpi/numa/hmat.c     |  5 +--
 include/linux/memory-tiers.h |  2 ++
 mm/memory-tiers.c            | 59 +++++++++++++++---------------------
 3 files changed, 28 insertions(+), 38 deletions(-)

diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
index 2c8ccc91ebe6..a2f9e7a4b479 100644
--- a/drivers/acpi/numa/hmat.c
+++ b/drivers/acpi/numa/hmat.c
@@ -940,10 +940,7 @@ static int hmat_set_default_dram_perf(void)
 	struct memory_target *target;
 	struct access_coordinate *attrs;
 
-	if (!default_dram_type)
-		return -EIO;
-
-	for_each_node_mask(nid, default_dram_type->nodes) {
+	for_each_node_mask(nid, default_dram_nodes) {
 		pxm = node_to_pxm(nid);
 		target = find_mem_target(pxm);
 		if (!target)
diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index 0d70788558f4..fa61ad9c4d75 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -38,6 +38,7 @@ struct access_coordinate;
 #ifdef CONFIG_NUMA
 extern bool numa_demotion_enabled;
 extern struct memory_dev_type *default_dram_type;
+extern nodemask_t default_dram_nodes __initdata;
 struct memory_dev_type *alloc_memory_type(int adistance);
 void put_memory_type(struct memory_dev_type *memtype);
 void init_node_memory_type(int node, struct memory_dev_type *default_type);
@@ -76,6 +77,7 @@ static inline bool node_is_toptier(int node)
 
 #define numa_demotion_enabled	false
 #define default_dram_type	NULL
+#define default_dram_nodes NODE_MASK_NONE
 /*
  * CONFIG_NUMA implementation returns non NULL error.
  */
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 6632102bd5c9..a19a90c3ad36 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -43,6 +43,7 @@ static LIST_HEAD(memory_tiers);
 static LIST_HEAD(default_memory_types);
 static struct node_memory_type_map node_memory_types[MAX_NUMNODES];
 struct memory_dev_type *default_dram_type;
+nodemask_t default_dram_nodes __initdata = NODE_MASK_NONE;
 
 static const struct bus_type memory_tier_subsys = {
 	.name = "memory_tiering",
@@ -671,28 +672,38 @@ EXPORT_SYMBOL_GPL(mt_put_memory_types);
 
 /*
  * This is invoked via `late_initcall()` to initialize memory tiers for
- * CPU-less memory nodes after driver initialization, which is
- * expected to provide `adistance` algorithms.
+ * memory nodes, both with and without CPUs. After the initialization of
+ * firmware and devices, adistance algorithms are expected to be provided.
  */
 static int __init memory_tier_late_init(void)
 {
 	int nid;
+	struct memory_tier *memtier;
 
+	get_online_mems();
 	guard(mutex)(&memory_tier_lock);
+	/*
+	 * Look at all the existing and uninitialized N_MEMORY nodes and
+	 * add them to default memory tier or to a tier if we already have
+	 * memory types assigned.
+	 */
 	for_each_node_state(nid, N_MEMORY) {
 		/*
-		 * Some device drivers may have initialized memory tiers
-		 * between `memory_tier_init()` and `memory_tier_late_init()`,
-		 * potentially bringing online memory nodes and
-		 * configuring memory tiers. Exclude them here.
+		 * Some device drivers may have initialized
+		 * memory tiers, potentially bringing memory nodes
+		 * online and configuring memory tiers.
+		 * Exclude them here.
 		 */
 		if (node_memory_types[nid].memtype)
 			continue;
 
-		set_node_memory_tier(nid);
+		memtier = set_node_memory_tier(nid);
+		if (IS_ERR(memtier))
+			/* Continue with memtiers we are able to setup. */
+			break;
 	}
-
 	establish_demotion_targets();
+	put_online_mems();
 
 	return 0;
 }
@@ -875,8 +886,7 @@ static int __meminit memtier_hotplug_callback(struct notifier_block *self,
 
 static int __init memory_tier_init(void)
 {
-	int ret, node;
-	struct memory_tier *memtier;
+	int ret;
 
 	ret = subsys_virtual_register(&memory_tier_subsys, NULL);
 	if (ret)
@@ -887,7 +897,8 @@ static int __init memory_tier_init(void)
 				GFP_KERNEL);
 	WARN_ON(!node_demotion);
 #endif
-	mutex_lock(&memory_tier_lock);
+
+	guard(mutex)(&memory_tier_lock);
 	/*
 	 * For now we can have 4 faster memory tiers with smaller adistance
 	 * than default DRAM tier.
@@ -897,29 +908,9 @@ static int __init memory_tier_init(void)
 	if (IS_ERR(default_dram_type))
 		panic("%s() failed to allocate default DRAM tier\n", __func__);
 
-	/*
-	 * Look at all the existing N_MEMORY nodes and add them to
-	 * default memory tier or to a tier if we already have memory
-	 * types assigned.
-	 */
-	for_each_node_state(node, N_MEMORY) {
-		if (!node_state(node, N_CPU))
-			/*
-			 * Defer memory tier initialization on
-			 * CPUless numa nodes. These will be initialized
-			 * after firmware and devices are initialized.
-			 */
-			continue;
-
-		memtier = set_node_memory_tier(node);
-		if (IS_ERR(memtier))
-			/*
-			 * Continue with memtiers we are able to setup
-			 */
-			break;
-	}
-	establish_demotion_targets();
-	mutex_unlock(&memory_tier_lock);
+	/* Record nodes with memory and CPU to set default DRAM performance. */
+	nodes_and(default_dram_nodes, node_states[N_MEMORY],
+		  node_states[N_CPU]);
 
 	hotplug_memory_notifier(memtier_hotplug_callback, MEMTIER_HOTPLUG_PRI);
 	return 0;
-- 
Ho-Ren (Jack) Chuang