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SubjectRe: [PATCH v2] mm/demotion: Expose memory tier details via sysfs
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On 8/30/22 12:01 PM, Wei Xu wrote:
> On Sun, Aug 28, 2022 at 11:08 PM Aneesh Kumar K.V
> <aneesh.kumar@linux.ibm.com> wrote:
>>
>> This patch adds /sys/devices/virtual/memory_tiering/ where all memory tier
>> related details can be found. All allocated memory tiers will be listed
>> there as /sys/devices/virtual/memory_tiering/memory_tierN/
>>
>> The nodes which are part of a specific memory tier can be listed via
>> /sys/devices/virtual/memory_tiering/memory_tierN/nodes
>>
>> The abstract distance range value of a specific memory tier can be listed via
>> /sys/devices/virtual/memory_tiering/memory_tierN/abstract_distance
>>
>> A directory hierarchy looks like
>> :/sys/devices/virtual/memory_tiering$ tree memory_tier4/
>> memory_tier4/
>> ├── abstract_distance
>> ├── nodes
>> ├── subsystem -> ../../../../bus/memory_tiering
>> └── uevent
>>
>> All toptier nodes are listed via
>> /sys/devices/virtual/memory_tiering/toptier_nodes
>>
>> :/sys/devices/virtual/memory_tiering$ cat toptier_nodes
>> 0,2
>> :/sys/devices/virtual/memory_tiering$ cat memory_tier4/nodes
>> 0,2
>> :/sys/devices/virtual/memory_tiering$ cat memory_tier4/abstract_distance
>> 512 - 639
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> ---
>> .../ABI/testing/sysfs-kernel-mm-memory-tiers | 41 +++++
>> mm/memory-tiers.c | 155 +++++++++++++++---
>> 2 files changed, 174 insertions(+), 22 deletions(-)
>> create mode 100644 Documentation/ABI/testing/sysfs-kernel-mm-memory-tiers
>>
>> diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-memory-tiers b/Documentation/ABI/testing/sysfs-kernel-mm-memory-tiers
>> new file mode 100644
>> index 000000000000..6955f69a4423
>> --- /dev/null
>> +++ b/Documentation/ABI/testing/sysfs-kernel-mm-memory-tiers
>> @@ -0,0 +1,41 @@
>> +What: /sys/devices/virtual/memory_tiering/
>> +Date: August 2022
>> +Contact: Linux memory management mailing list <linux-mm@kvack.org>
>> +Description: A collection of all the memory tiers allocated.
>> +
>> + Individual memory tier details are contained in subdirectories
>> + named by the abstract distance of the memory tier.
>> +
>> + /sys/devices/virtual/memory_tiering/memory_tierN/
>> +
>> +
>> +What: /sys/devices/virtual/memory_tiering/memory_tierN/
>> + /sys/devices/virtual/memory_tiering/memory_tierN/abstract_distance
>> + /sys/devices/virtual/memory_tiering/memory_tierN/nodes
>> +Date: August 2022
>> +Contact: Linux memory management mailing list <linux-mm@kvack.org>
>> +Description: Directory with details of a specific memory tier
>> +
>> + This is the directory containing information about a particular
>> + memory tier, memtierN, where N is derived based on abstract distance.
>> +
>> + A smaller value of N implies a higher (faster) memory tier in the
>> + hierarchy.
>
> Given that abstract_distance is provided, it would be more flexible if
> we don't commit to the interface where N in memtierN also indicates
> the memory tier ordering.


IIUC this is one of the request that Johannes had ie, to be able to understand the
memory tier hierarchy based on memtier name.

>> +
>> + abstract_distance: The abstract distance range this specific memory
>> + tier maps to.
>
> I still think the name of "abstract distance" is kind of confusing
> because it is not clear what is the other object that this distance
> value is relative to. Do we have to expose this value at this point
> if N in memtierN can already indicate the memory tier ordering?
>

I do agree that abstract distance is confusing. But IIUC we agreed that it is much better
than other names suggested and is closer to already understood "numa distance" term.

https://lore.kernel.org/linux-mm/YuLF%2FGG8x5lQvg%2Ff@cmpxchg.org/


>> + nodes: NUMA nodes that are part of this memory tier.
>> +
>> +
>> +What: /sys/devices/virtual/memory_tiering/toptier_nodes
>> +Date: August 2022
>> +Contact: Linux memory management mailing list <linux-mm@kvack.org>
>> +Description: Toptier node mask
>> +
>> + A toptier is defined as the memory tier from which memory promotion
>> + is not done by the kernel.
>> +
>> + toptier_nodes: NUMA nodes that are part of all the memory tiers
>> + above a topier tier.
>
> Nit: topier -> toptier
>
> toptier_nodes should be the union of NUMA nodes that are part of each
> toptier, not above a toptier, right?
>

I will update the wording. Yes. it is the union of NUMA nodes that are
part of each toptier.

>> +
>> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
>> index c4bd6d052a33..d4648d4e4d54 100644
>> --- a/mm/memory-tiers.c
>> +++ b/mm/memory-tiers.c
>> @@ -19,6 +19,7 @@ struct memory_tier {
>> * adistance_start .. adistance_start + MEMTIER_CHUNK_SIZE
>> */
>> int adistance_start;
>> + struct device dev;
>> /* All the nodes that are part of all the lower memory tiers. */
>> nodemask_t lower_tier_mask;
>> };
>> @@ -36,6 +37,13 @@ static DEFINE_MUTEX(memory_tier_lock);
>> static LIST_HEAD(memory_tiers);
>> static struct node_memory_type_map node_memory_types[MAX_NUMNODES];
>> static struct memory_dev_type *default_dram_type;
>> +
>> +#define to_memory_tier(device) container_of(device, struct memory_tier, dev)
>> +static struct bus_type memory_tier_subsys = {
>> + .name = "memory_tiering",
>> + .dev_name = "memory_tier",
>> +};
>> +
>> #ifdef CONFIG_MIGRATION
>> static int top_tier_adistance;
>> /*
>> @@ -98,8 +106,73 @@ static int top_tier_adistance;
>> static struct demotion_nodes *node_demotion __read_mostly;
>> #endif /* CONFIG_MIGRATION */
>>
>> +static __always_inline nodemask_t get_memtier_nodemask(struct memory_tier *memtier)
>> +{
>> + nodemask_t nodes = NODE_MASK_NONE;
>> + struct memory_dev_type *memtype;
>> +
>> + list_for_each_entry(memtype, &memtier->memory_types, tier_sibiling)
>> + nodes_or(nodes, nodes, memtype->nodes);
>> +
>> + return nodes;
>> +}
>> +
>> +static void memory_tier_device_release(struct device *dev)
>> +{
>> + struct memory_tier *tier = to_memory_tier(dev);
>> + /*
>> + * synchronize_rcu in clear_node_memory_tier makes sure
>> + * we don't have rcu access to this memory tier.
>> + */
>> + kfree(tier);
>> +}
>> +
>> +static ssize_t nodes_show(struct device *dev,
>> + struct device_attribute *attr, char *buf)
>> +{
>> + int ret;
>> + nodemask_t nmask;
>> +
>> + mutex_lock(&memory_tier_lock);
>> + nmask = get_memtier_nodemask(to_memory_tier(dev));
>> + ret = sysfs_emit(buf, "%*pbl\n", nodemask_pr_args(&nmask));
>> + mutex_unlock(&memory_tier_lock);
>> + return ret;
>> +}
>> +static DEVICE_ATTR_RO(nodes);
>> +
>> +static ssize_t abstract_distance_show(struct device *dev,
>> + struct device_attribute *attr, char *buf)
>> +{
>> + int ret;
>> + struct memory_tier *memtier = to_memory_tier(dev);
>> +
>> + mutex_lock(&memory_tier_lock);
>> + ret = sysfs_emit(buf, "%d - %d\n", memtier->adistance_start,
>> + memtier->adistance_start + MEMTIER_CHUNK_SIZE - 1);
>> + mutex_unlock(&memory_tier_lock);
>> + return ret;
>> +}
>> +static DEVICE_ATTR_RO(abstract_distance);
>> +
>> +static struct attribute *memtier_dev_attrs[] = {
>> + &dev_attr_nodes.attr,
>> + &dev_attr_abstract_distance.attr,
>> + NULL
>> +};
>> +
>> +static const struct attribute_group memtier_dev_group = {
>> + .attrs = memtier_dev_attrs,
>> +};
>> +
>> +static const struct attribute_group *memtier_dev_groups[] = {
>> + &memtier_dev_group,
>> + NULL
>> +};
>> +
>> static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memtype)
>> {
>> + int ret;
>> bool found_slot = false;
>> struct memory_tier *memtier, *new_memtier;
>> int adistance = memtype->adistance;
>> @@ -123,15 +196,14 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty
>>
>> list_for_each_entry(memtier, &memory_tiers, list) {
>> if (adistance == memtier->adistance_start) {
>> - list_add(&memtype->tier_sibiling, &memtier->memory_types);
>> - return memtier;
>> + goto link_memtype;
>> } else if (adistance < memtier->adistance_start) {
>> found_slot = true;
>> break;
>> }
>> }
>>
>> - new_memtier = kmalloc(sizeof(struct memory_tier), GFP_KERNEL);
>> + new_memtier = kzalloc(sizeof(struct memory_tier), GFP_KERNEL);
>> if (!new_memtier)
>> return ERR_PTR(-ENOMEM);
>>
>> @@ -142,8 +214,23 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty
>> list_add_tail(&new_memtier->list, &memtier->list);
>> else
>> list_add_tail(&new_memtier->list, &memory_tiers);
>> - list_add(&memtype->tier_sibiling, &new_memtier->memory_types);
>> - return new_memtier;
>> +
>> + new_memtier->dev.id = adistance >> MEMTIER_CHUNK_BITS;
>> + new_memtier->dev.bus = &memory_tier_subsys;
>> + new_memtier->dev.release = memory_tier_device_release;
>> + new_memtier->dev.groups = memtier_dev_groups;
>> +
>> + ret = device_register(&new_memtier->dev);
>> + if (ret) {
>> + list_del(&memtier->list);
>> + put_device(&memtier->dev);
>> + return ERR_PTR(ret);
>> + }
>> + memtier = new_memtier;
>> +
>> +link_memtype:
>> + list_add(&memtype->tier_sibiling, &memtier->memory_types);
>> + return memtier;
>> }
>>
>> static struct memory_tier *__node_get_memory_tier(int node)
>> @@ -275,17 +362,6 @@ static void disable_all_demotion_targets(void)
>> synchronize_rcu();
>> }
>>
>> -static __always_inline nodemask_t get_memtier_nodemask(struct memory_tier *memtier)
>> -{
>> - nodemask_t nodes = NODE_MASK_NONE;
>> - struct memory_dev_type *memtype;
>> -
>> - list_for_each_entry(memtype, &memtier->memory_types, tier_sibiling)
>> - nodes_or(nodes, nodes, memtype->nodes);
>> -
>> - return nodes;
>> -}
>> -
>> /*
>> * Find an automatic demotion target for all memory
>> * nodes. Failing here is OK. It might just indicate
>> @@ -432,11 +508,7 @@ static struct memory_tier *set_node_memory_tier(int node)
>> 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);
>> + device_unregister(&memtier->dev);
>> }
>>
>> static bool clear_node_memory_tier(int node)
>> @@ -563,11 +635,50 @@ static int __meminit memtier_hotplug_callback(struct notifier_block *self,
>> return notifier_from_errno(0);
>> }
>>
>> +static ssize_t toptier_nodes_show(struct device *dev,
>> + struct device_attribute *attr, char *buf)
>> +{
>> + int ret;
>> + nodemask_t nmask, top_tier_mask = NODE_MASK_NONE;
>> + struct memory_tier *memtier = to_memory_tier(dev);
>> +
>> + mutex_lock(&memory_tier_lock);
>> + list_for_each_entry(memtier, &memory_tiers, list) {
>> + if (memtier->adistance_start >= top_tier_adistance)
>
> It is kind of confusing that a tier with top_tier_adistance is not
> considered as a toptier. Can we redefine top_tier_adistance to be the
> inclusive upper bound of toptiers?
>

Agreed. I will fix that up by doing

top_tier_adistance = memtier->adistance_start + MEMTIER_CHUNK_SIZE - 1;


>> + break;
>> + nmask = get_memtier_nodemask(memtier);
>> + nodes_or(top_tier_mask, top_tier_mask, nmask);
>> + }
>> +
>> + ret = sysfs_emit(buf, "%*pbl\n", nodemask_pr_args(&top_tier_mask));
>> + mutex_unlock(&memory_tier_lock);
>> + return ret;
>> +}
>> +static DEVICE_ATTR_RO(toptier_nodes);
>> +
>> +static struct attribute *memtier_subsys_attrs[] = {
>> + &dev_attr_toptier_nodes.attr,
>> + NULL
>> +};
>> +
>> +static const struct attribute_group memtier_subsys_group = {
>> + .attrs = memtier_subsys_attrs,
>> +};
>> +
>> +static const struct attribute_group *memtier_subsys_groups[] = {
>> + &memtier_subsys_group,
>> + NULL
>> +};
>> +
>> static int __init memory_tier_init(void)
>> {
>> - int node;
>> + int ret, node;
>> struct memory_tier *memtier;
>>
>> + ret = subsys_virtual_register(&memory_tier_subsys, memtier_subsys_groups);
>> + if (ret)
>> + panic("%s() failed to register memory tier subsystem\n", __func__);
>> +
>> #ifdef CONFIG_MIGRATION
>> node_demotion = kcalloc(nr_node_ids, sizeof(struct demotion_nodes),
>> GFP_KERNEL);
>> --
>> 2.37.2
>>

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