Date:   Tue, 26 Jul 2022 10:13:03 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        Wei Xu <weixugc@...gle.com>, Yang Shi <shy828301@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim C Chen <tim.c.chen@...el.com>,
        Michal Hocko <mhocko@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hesham Almatary <hesham.almatary@...wei.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alistair Popple <apopple@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Johannes Weiner <hannes@...xchg.org>, jvgediya.oss@...il.com
Subject: Re: [PATCH v10 4/8] mm/demotion/dax/kmem: Set node's performance
 level to MEMTIER_PERF_LEVEL_PMEM

Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com> writes:

> On 7/25/22 2:05 PM, Huang, Ying wrote:
>> Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com> writes:
>> 
>>> On 7/25/22 12:07 PM, Huang, Ying wrote:
>>>> "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> writes:
>>>>
>>>>> By default, all nodes are assigned to the default memory tier which
>>>>> is the memory tier designated for nodes with DRAM
>>>>>
>>>>> Set dax kmem device node's tier to slower memory tier by assigning
>>>>> performance level to MEMTIER_PERF_LEVEL_PMEM. PMEM tier
>>>>> appears below the default memory tier in demotion order.
>>>>>
>>>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
>>>>> ---
>>>>>  arch/powerpc/platforms/pseries/papr_scm.c | 41 ++++++++++++++++++++---
>>>>>  drivers/acpi/nfit/core.c                  | 41 ++++++++++++++++++++++-
>>>>>  2 files changed, 76 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
>>>>> index 82cae08976bc..3b6164418d6f 100644
>>>>> --- a/arch/powerpc/platforms/pseries/papr_scm.c
>>>>> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
>>>>> @@ -14,6 +14,8 @@
>>>>>  #include <linux/delay.h>
>>>>>  #include <linux/seq_buf.h>
>>>>>  #include <linux/nd.h>
>>>>> +#include <linux/memory.h>
>>>>> +#include <linux/memory-tiers.h>
>>>>>  
>>>>>  #include <asm/plpar_wrappers.h>
>>>>>  #include <asm/papr_pdsm.h>
>>>>> @@ -98,6 +100,7 @@ struct papr_scm_priv {
>>>>>  	bool hcall_flush_required;
>>>>>  
>>>>>  	uint64_t bound_addr;
>>>>> +	int target_node;
>>>>>  
>>>>>  	struct nvdimm_bus_descriptor bus_desc;
>>>>>  	struct nvdimm_bus *bus;
>>>>> @@ -1278,6 +1281,7 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>>>>>  	p->bus_desc.module = THIS_MODULE;
>>>>>  	p->bus_desc.of_node = p->pdev->dev.of_node;
>>>>>  	p->bus_desc.provider_name = kstrdup(p->pdev->name, GFP_KERNEL);
>>>>> +	p->target_node = dev_to_node(&p->pdev->dev);
>>>>>  
>>>>>  	/* Set the dimm command family mask to accept PDSMs */
>>>>>  	set_bit(NVDIMM_FAMILY_PAPR, &p->bus_desc.dimm_family_mask);
>>>>> @@ -1322,7 +1326,7 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>>>>>  	mapping.size = p->blocks * p->block_size; // XXX: potential overflow?
>>>>>  
>>>>>  	memset(&ndr_desc, 0, sizeof(ndr_desc));
>>>>> -	target_nid = dev_to_node(&p->pdev->dev);
>>>>> +	target_nid = p->target_node;
>>>>>  	online_nid = numa_map_to_online_node(target_nid);
>>>>>  	ndr_desc.numa_node = online_nid;
>>>>>  	ndr_desc.target_node = target_nid;
>>>>> @@ -1582,15 +1586,42 @@ static struct platform_driver papr_scm_driver = {
>>>>>  	},
>>>>>  };
>>>>>  
>>>>> +static int papr_scm_callback(struct notifier_block *self,
>>>>> +			     unsigned long action, void *arg)
>>>>> +{
>>>>> +	struct memory_notify *mnb = arg;
>>>>> +	int nid = mnb->status_change_nid;
>>>>> +	struct papr_scm_priv *p;
>>>>> +
>>>>> +	if (nid == NUMA_NO_NODE || action != MEM_ONLINE)
>>>>> +		return NOTIFY_OK;
>>>>> +
>>>>> +	mutex_lock(&papr_ndr_lock);
>>>>> +	list_for_each_entry(p, &papr_nd_regions, region_list) {
>>>>> +		if (p->target_node == nid) {
>>>>> +			node_devices[nid]->perf_level = MEMTIER_PERF_LEVEL_PMEM;
>>>>> +			break;
>>>>> +		}
>>>>> +	}
>>>>> +
>>>>> +	mutex_unlock(&papr_ndr_lock);
>>>>> +	return NOTIFY_OK;
>>>>> +}
>>>>> +
>>>>>  static int __init papr_scm_init(void)
>>>>>  {
>>>>>  	int ret;
>>>>>  
>>>>>  	ret = platform_driver_register(&papr_scm_driver);
>>>>> -	if (!ret)
>>>>> -		mce_register_notifier(&mce_ue_nb);
>>>>> -
>>>>> -	return ret;
>>>>> +	if (ret)
>>>>> +		return ret;
>>>>> +	mce_register_notifier(&mce_ue_nb);
>>>>> +	/*
>>>>> +	 * register a memory hotplug notifier at prio 2 so that we
>>>>> +	 * can update the perf level for the node.
>>>>> +	 */
>>>>> +	hotplug_memory_notifier(papr_scm_callback, MEMTIER_HOTPLUG_PRIO + 1);
>>>>> +	return 0;
>>>>>  }
>>>>>  module_init(papr_scm_init);
>>>>>  
>>>>> diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
>>>>> index ae5f4acf2675..7ea1017ef790 100644
>>>>> --- a/drivers/acpi/nfit/core.c
>>>>> +++ b/drivers/acpi/nfit/core.c
>>>>> @@ -15,6 +15,8 @@
>>>>>  #include <linux/sort.h>
>>>>>  #include <linux/io.h>
>>>>>  #include <linux/nd.h>
>>>>> +#include <linux/memory.h>
>>>>> +#include <linux/memory-tiers.h>
>>>>>  #include <asm/cacheflush.h>
>>>>>  #include <acpi/nfit.h>
>>>>>  #include "intel.h"
>>>>> @@ -3470,6 +3472,39 @@ static struct acpi_driver acpi_nfit_driver = {
>>>>>  	},
>>>>>  };
>>>>>  
>>>>> +static int nfit_callback(struct notifier_block *self,
>>>>> +			 unsigned long action, void *arg)
>>>>> +{
>>>>> +	bool found = false;
>>>>> +	struct memory_notify *mnb = arg;
>>>>> +	int nid = mnb->status_change_nid;
>>>>> +	struct nfit_spa *nfit_spa;
>>>>> +	struct acpi_nfit_desc *acpi_desc;
>>>>> +
>>>>> +	if (nid == NUMA_NO_NODE || action != MEM_ONLINE)
>>>>> +		return NOTIFY_OK;
>>>>> +
>>>>> +	mutex_lock(&acpi_desc_lock);
>>>>> +	list_for_each_entry(acpi_desc, &acpi_descs, list) {
>>>>> +		mutex_lock(&acpi_desc->init_mutex);
>>>>> +		list_for_each_entry(nfit_spa, &acpi_desc->spas, list) {
>>>>> +			struct acpi_nfit_system_address *spa = nfit_spa->spa;
>>>>> +			int target_node = pxm_to_node(spa->proximity_domain);
>>>>> +
>>>>> +			if (target_node == nid) {
>>>>> +				node_devices[nid]->perf_level = MEMTIER_PERF_LEVEL_PMEM;
>>>>> +				found = true;
>>>>> +				break;
>>>>> +			}
>>>>> +		}
>>>>> +		mutex_unlock(&acpi_desc->init_mutex);
>>>>> +		if (found)
>>>>> +			break;
>>>>> +	}
>>>>> +	mutex_unlock(&acpi_desc_lock);
>>>>> +	return NOTIFY_OK;
>>>>> +}
>>>>> +
>>>>>  static __init int nfit_init(void)
>>>>>  {
>>>>>  	int ret;
>>>>> @@ -3509,7 +3544,11 @@ static __init int nfit_init(void)
>>>>>  		nfit_mce_unregister();
>>>>>  		destroy_workqueue(nfit_wq);
>>>>>  	}
>>>>> -
>>>>> +	/*
>>>>> +	 * register a memory hotplug notifier at prio 2 so that we
>>>>> +	 * can update the perf level for the node.
>>>>> +	 */
>>>>> +	hotplug_memory_notifier(nfit_callback, MEMTIER_HOTPLUG_PRIO + 1);
>>>>>  	return ret;
>>>>>  
>>>>>  }
>>>>
>>>> I don't think that it's a good idea to set perf_level of a memory device
>>>> (node) via NFIT only.
>>>
>>>>
>>>> For example, we may prefer HMAT over NFIT when it's available.  So the
>>>> perf_level should be set in dax/kmem.c based on information provided by
>>>> ACPI or other information sources.  ACPI can provide some functions/data
>>>> structures to let drivers (like dax/kmem.c) to query the properties of
>>>> the memory device (node).
>>>>
>>>
>>> I was trying to make it architecture specific so that we have a placeholder
>>> to fine-tune this better. For example, ppc64 will look at device tree
>>> details to find the performance level and x86 will look at ACPI data structure.
>>> Adding that hotplug callback in dax/kmem will prevent that architecture-specific
>>> customization? 
>>>
>>> I would expect that callback to move to the generic ACPI layer so that even
>>> firmware managed CXL devices can be added to a lower tier?  I don't understand
>>> ACPI enough to find the right abstraction for that hotplug callback. 
>> 
>> I'm OK for this to be architecture specific.
>> 
>> But ACPI NFIT isn't enough for x86.  For example, PMEM can be added to a
>> virtual machine as normal memory nodes without NFIT.  Instead, PMEM is
>> marked via "memmap=<nn>G!<ss>G" or "efi_fake_mem=<nn>G@<ss>G:0x40000",
>> and dax/kmem.c is used to hot-add the memory.
>> 
>> So, before a more sophisticated version is implemented for x86.  The
>> simplest version as I suggested below works even better.
>> 
>>>> As the simplest first version, this can be just hard coded.
>>>>
>>>
>>> If you are suggesting to not use hotplug callback, one of the challenge was node_devices[nid]
>>> get allocated pretty late when we try to online the node. 
>> 
>> As the simplest first version, this can be as simple as,
>> 
>> /* dax/kmem.c */
>> static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>> {
>> 	node_devices[dev_dax->target_node]->perf_level = MEMTIER_PERF_LEVEL_PMEM;
>> 	/* add_memory_driver_managed() */
>> }
>> 
>> To be compatible with ppc64 version, how about make dev_dax_kmem_probe()
>> set perf_level only if it's uninitialized?
>
> That will result in kernel crash because node_devices[dev_dax->target_node] is not initialized there. 
>
> it get allocated in add_memory_resource -> __try_online_node ->
> register_one_node -> __register_one_node -> node_devices[nid] =
> kzalloc(sizeof(struct node), GFP_KERNEL);

Ah, right!  So we need some other way to do that, for example, a global
array as follows,

  int node_perf_levels[MAX_NUMNODES];

And, I think that we need to consider the memory type here too.  As
suggested by Johannes, memory type describes a set of memory devices
(NUMA nodes) with same performance character (that is, abstract distance
or perf level).  The data structure can be something as follows,

  struct memory_type {
        int perf_level;
        struct list_head tier_sibling;
        nodemask_t nodes;
  };

The memory_type should be created and managed by the device drivers
(e.g., dax/kmem) which manages the memory devices.  In the future, we
will represent it in sysfs, and a per-memory_type knob will be provided
to offset the perf_level of all memory devices managed by the
memory_type.

With memory_type, the memory_tier becomes,

  struct memory_tier {
        int perf_level_start;
        struct list_head sibling;
        struct list_head memory_types;
  };

And we need an array to map from nid to memory_type, e.g., as follows,

  struct memory_type *node_memory_types[MAX_NUMNODES];

We need to manage the memory_type in device drivers, instead of ACPI or
device tree callbacks.

Because memory_type is an important part of the explicit memory tier
implementation and may influence the design, I suggest to include it in
the implementation now.  It appears not too complex anyway.

Best Regards,
Huang, Ying

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