Message-ID: <3f67b269-b69f-86a1-db1f-ba2408949b38@linux.ibm.com>
Date:   Mon, 25 Jul 2022 14:12:25 +0530
From:   Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
To:     "Huang, Ying" <ying.huang@...el.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

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);

-aneesh

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