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

Alistair Popple
2023-08-21T12:04:50Z

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

> Alistair Popple <apopple@nvidia.com> writes:
>
>> 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.
>
> If it's useful, we can move kmem_find_alloc_memory_type() to
> memory-tier.c after some revision. But I tend to move it after we have
> the second user. What do you think about that?

Usually I would agree, but this series already introduces a general
interface for calculating adist even though there's only one user and
implementation. So if we're going to add a general interface I think it
would be better to make it more usable now rather than after variations
of it have been cut and pasted into other drivers.