Re: [PATCH RESEND 4/4] dax, kmem: calculate abstract distance with general interface

Alistair Popple
2023-07-25T03:13:34Z

Huang Ying <ying.huang@intel.com> writes:

> Previously, a fixed abstract distance MEMTIER_DEFAULT_DAX_ADISTANCE is
> used for slow memory type in kmem driver. This limits the usage of
> kmem driver, for example, it cannot be used for HBM (high bandwidth
> memory).
>
> So, we use the general abstract distance calculation mechanism in kmem
> drivers to get more accurate abstract distance on systems with proper
> support. The original MEMTIER_DEFAULT_DAX_ADISTANCE is used as
> fallback only.
>
> Now, multiple memory types may be managed by kmem. These memory types
> are put into the "kmem_memory_types" list and protected by
> kmem_memory_type_lock.

See below but I wonder if kmem_memory_types could be a common helper
rather than kdax specific?

> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Cc: Wei Xu <weixugc@google.com>
> Cc: Alistair Popple <apopple@nvidia.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Davidlohr Bueso <dave@stgolabs.net>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Yang Shi <shy828301@gmail.com>
> Cc: Rafael J Wysocki <rafael.j.wysocki@intel.com>
> ---
> drivers/dax/kmem.c | 54 +++++++++++++++++++++++++++---------
> include/linux/memory-tiers.h | 2 ++
> mm/memory-tiers.c | 2 +-
> 3 files changed, 44 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 898ca9505754..837165037231 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -49,14 +49,40 @@ struct dax_kmem_data {
> struct resource *res[];
> };
>
> -static struct memory_dev_type *dax_slowmem_type;
> +static DEFINE_MUTEX(kmem_memory_type_lock);
> +static LIST_HEAD(kmem_memory_types);
> +
> +static struct memory_dev_type *kmem_find_alloc_memorty_type(int adist)
> +{
> + bool found = false;
> + struct memory_dev_type *mtype;
> +
> + mutex_lock(&kmem_memory_type_lock);
> + list_for_each_entry(mtype, &kmem_memory_types, list) {
> + if (mtype->adistance == adist) {
> + found = true;
> + break;
> + }
> + }
> + if (!found) {
> + mtype = alloc_memory_type(adist);
> + if (!IS_ERR(mtype))
> + list_add(&mtype->list, &kmem_memory_types);
> + }
> + mutex_unlock(&kmem_memory_type_lock);
> +
> + return mtype;
> +}
> +
> static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> {
> struct device *dev = &dev_dax->dev;
> unsigned long total_len = 0;
> struct dax_kmem_data *data;
> + struct memory_dev_type *mtype;
> int i, rc, mapped = 0;
> int numa_node;
> + int adist = MEMTIER_DEFAULT_DAX_ADISTANCE;
>
> /*
> * Ensure good NUMA information for the persistent memory.
> @@ -71,6 +97,11 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> return -EINVAL;
> }
>
> + mt_calc_adistance(numa_node, &adist);
> + mtype = kmem_find_alloc_memorty_type(adist);
> + if (IS_ERR(mtype))
> + return PTR_ERR(mtype);
> +

I wrote my own quick and dirty module to test this and wrote basically
the same code sequence.

I notice your using a list of memory types here though. I think it would
be nice to have a common helper that other users could call to do the
mt_calc_adistance() / kmem_find_alloc_memory_type() /
init_node_memory_type() sequence and cleanup as my naive approach would
result in a new memory_dev_type per device even though adist might be
the same. A common helper would make it easy to de-dup those.

> for (i = 0; i < dev_dax->nr_range; i++) {
> struct range range;
>
> @@ -88,7 +119,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> return -EINVAL;
> }
>
> - init_node_memory_type(numa_node, dax_slowmem_type);
> + init_node_memory_type(numa_node, mtype);
>
> rc = -ENOMEM;
> data = kzalloc(struct_size(data, res, dev_dax->nr_range), GFP_KERNEL);
> @@ -167,7 +198,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> err_res_name:
> kfree(data);
> err_dax_kmem_data:
> - clear_node_memory_type(numa_node, dax_slowmem_type);
> + clear_node_memory_type(numa_node, mtype);
> return rc;
> }
>
> @@ -219,7 +250,7 @@ static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
> * for that. This implies this reference will be around
> * till next reboot.
> */
> - clear_node_memory_type(node, dax_slowmem_type);
> + clear_node_memory_type(node, NULL);
> }
> }
> #else
> @@ -251,12 +282,6 @@ static int __init dax_kmem_init(void)
> if (!kmem_name)
> return -ENOMEM;
>
> - dax_slowmem_type = alloc_memory_type(MEMTIER_DEFAULT_DAX_ADISTANCE);
> - if (IS_ERR(dax_slowmem_type)) {
> - rc = PTR_ERR(dax_slowmem_type);
> - goto err_dax_slowmem_type;
> - }
> -
> rc = dax_driver_register(&device_dax_kmem_driver);
> if (rc)
> goto error_dax_driver;
> @@ -264,18 +289,21 @@ static int __init dax_kmem_init(void)
> return rc;
>
> error_dax_driver:
> - destroy_memory_type(dax_slowmem_type);
> -err_dax_slowmem_type:
> kfree_const(kmem_name);
> return rc;
> }
>
> static void __exit dax_kmem_exit(void)
> {
> + struct memory_dev_type *mtype, *mtn;
> +
> dax_driver_unregister(&device_dax_kmem_driver);
> if (!any_hotremove_failed)
> kfree_const(kmem_name);
> - destroy_memory_type(dax_slowmem_type);
> + list_for_each_entry_safe(mtype, mtn, &kmem_memory_types, list) {
> + list_del(&mtype->list);
> + destroy_memory_type(mtype);
> + }
> }
>
> MODULE_AUTHOR("Intel Corporation");
> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> index 9377239c8d34..aca22220cb5c 100644
> --- a/include/linux/memory-tiers.h
> +++ b/include/linux/memory-tiers.h
> @@ -24,6 +24,8 @@ struct memory_tier;
> struct memory_dev_type {
> /* list of memory types that are part of same tier as this type */
> struct list_head tier_sibiling;
> + /* list of memory types that are managed by one driver */
> + struct list_head list;
> /* abstract distance for this specific memory type */
> int adistance;
> /* Nodes of same abstract distance */
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 9a734ef2edfb..38005c60fa2d 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -581,7 +581,7 @@ 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 == memtype)
> + if (node_memory_types[node].memtype == memtype || !memtype)
> node_memory_types[node].map_count--;
> /*
> * If we umapped all the attached devices to this node,