[PATCH v3] memory tier: consolidate the initialization of memory tiers

[Ho-Ren (Jack) Chuang]

The current memory tier initialization process is distributed across
two different functions, memory_tier_init() and memory_tier_late_init().
This design is hard to maintain. Thus, this patch is proposed to reduce
the possible code paths by consolidating different
initialization patches into one.

The earlier discussion with Jonathan and Ying is listed here:
https://lore.kernel.org/lkml/20240405150244.00004b49@Huawei.com/

If we want to put these two initializations together, they must be
placed together in the later function. Because only at that time,
the HMAT information will be ready, adist between nodes can be
calculated, and memory tiering can be established based on the adist.
So we position the initialization at memory_tier_init() to the
memory_tier_late_init() call. Moreover, it's natural to keep
memory_tier initialization in drivers at device_initcall() level.

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.

This patchset is based on commits <cf93be18fa1b> ("memory tier: create
CPUless memory tiers after obtaining HMAT info") and
<a72a30af550c> ("memory tier: dax/kmem: introduce an abstract layer for
finding, allocating, and putting memory types"):
[0/2] 
https://lkml.kernel.org/r/20240405000707.2670063-1-horenchuang@bytedance.com
[1/2] 
https://lkml.kernel.org/r/20240405000707.2670063-2-horenchuang@bytedance.com
[1/2] 
https://lkml.kernel.org/r/20240405000707.2670063-3-horenchuang@bytedance.com

Signed-off-by: Ho-Ren (Jack) Chuang <horenchuang@bytedance.com>
Suggested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
- v3:
 * Combine the cover letter and the patch.
 * Remove extern default_dram_type
 * Remove __initdata in a extern variable
 * Roll back coding style, fix comment description
- v2:
 Thanks to Huang, Ying's and Andrew's comments
 * Add a cover letter
 * Add Suggested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
 * Add get/put_online_mems() protection in memory_tier_late_init()
 * If memtype is set, skip initializing its node
 * Remove redundant code/comments or rewrite code in a cleaner manner
 * https://lore.kernel.org/all/20240628060925.303309-1-horen.chuang@linux.dev/
- v1:
 * https://lore.kernel.org/all/20240621044833.3953055-1-horen.chuang@linux.dev/

- Open to discussion:
 * Should we use `continue` or `break` if set_node_memory_tier() fails in
   memory_tier_late_init()? I've changed it to `continue` in v3.
 * Compute the default_dram_nodes mask in hmat when needed? Currently,
   it still remains in memory-tiers.c
 * Instead of using guard(mutex)(), use mutex_lock() as it was to make a
   cleaner diff?

Thanks,
Ho-Ren (Jack) Chuang

 drivers/acpi/numa/hmat.c     |  5 +---
 include/linux/memory-tiers.h |  2 ++
 mm/memory-tiers.c            | 54 ++++++++++++++----------------------
 3 files changed, 24 insertions(+), 37 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..0dc0cf2863e2 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;
 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..4775b3a3dabe 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 +672,35 @@ 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);
+
+       /* Assign each uninitialized N_MEMORY node to a memory tier. */
        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;
        }
 
        establish_demotion_targets();
+       put_online_mems();
 
        return 0;
 }
@@ -875,8 +883,7 @@ 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 +894,8 @@ 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 +905,9 @@ 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