linux-kernel - Re: [PATCH v10 3/8] mm/demotion: Add hotplug callbacks to handle new numa node onlined

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Date:   Tue, 26 Jul 2022 12:03:58 +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 3/8] mm/demotion: Add hotplug callbacks to handle
 new numa node onlined

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

> If the new NUMA node onlined doesn't have a performance level assigned,
> the kernel adds the NUMA node to default memory tier.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> ---
>  include/linux/memory-tiers.h |  1 +
>  mm/memory-tiers.c            | 75 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 76 insertions(+)
>
> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> index ef380a39db3a..3d5f14d57ae6 100644
> --- a/include/linux/memory-tiers.h
> +++ b/include/linux/memory-tiers.h
> @@ -14,6 +14,7 @@
>  #define MEMTIER_PERF_LEVEL_DRAM	(1 << (MEMTIER_CHUNK_BITS + 2))
>  /* leave one tier below this slow pmem */
>  #define MEMTIER_PERF_LEVEL_PMEM	(1 << MEMTIER_CHUNK_BITS)
> +#define MEMTIER_HOTPLUG_PRIO	100
>  
>  extern bool numa_demotion_enabled;
>  
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 41a21cc5ae55..cc3a47ec18e4 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -5,6 +5,7 @@
>  #include <linux/lockdep.h>
>  #include <linux/moduleparam.h>
>  #include <linux/node.h>
> +#include <linux/memory.h>
>  #include <linux/memory-tiers.h>
>  
>  struct memory_tier {
> @@ -64,6 +65,78 @@ static struct memory_tier *find_create_memory_tier(unsigned int perf_level)
>  	return new_memtier;
>  }
>  
> +static struct memory_tier *__node_get_memory_tier(int node)
> +{
> +	struct memory_tier *memtier;
> +
> +	list_for_each_entry(memtier, &memory_tiers, list) {
> +		if (node_isset(node, memtier->nodelist))
> +			return memtier;
> +	}
> +	return NULL;
> +}
> +
> +static void init_node_memory_tier(int node)

set_node_memory_tier()?

> +{
> +	int perf_level;
> +	struct memory_tier *memtier;
> +
> +	mutex_lock(&memory_tier_lock);
> +
> +	memtier = __node_get_memory_tier(node);
> +	if (!memtier) {
> +		perf_level = node_devices[node]->perf_level;
> +		memtier = find_create_memory_tier(perf_level);
> +		node_set(node, memtier->nodelist);
> +	}
> +	mutex_unlock(&memory_tier_lock);
> +}
> +
> +static void clear_node_memory_tier(int node)
> +{
> +	struct memory_tier *memtier;
> +
> +	mutex_lock(&memory_tier_lock);
> +	memtier = __node_get_memory_tier(node);
> +	if (memtier)
> +		node_clear(node, memtier->nodelist);

When memtier->nodelist becomes empty, we need to free memtier?

> +	mutex_unlock(&memory_tier_lock);
> +}
> +
> +/*
> + * This runs whether reclaim-based migration is enabled or not,
> + * which ensures that the user can turn reclaim-based migration
> + * at any time without needing to recalculate migration targets.
> + */

The comments doesn't apply here.

> +static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
> +						 unsigned long action, void *_arg)

Now we are building memory tiers instead of working on demotion.  So I
think we should rename the function to memtier_hotplug_callback().

> +{
> +	struct memory_notify *arg = _arg;
> +
> +	/*
> +	 * Only update the node migration order when a node is
> +	 * changing status, like online->offline.
> +	 */
> +	if (arg->status_change_nid < 0)
> +		return notifier_from_errno(0);
> +
> +	switch (action) {
> +	case MEM_OFFLINE:
> +		clear_node_memory_tier(arg->status_change_nid);
> +		break;
> +	case MEM_ONLINE:
> +		init_node_memory_tier(arg->status_change_nid);
> +		break;
> +	}
> +
> +	return notifier_from_errno(0);
> +}
> +
> +static void __init migrate_on_reclaim_init(void)
> +{
> +	hotplug_memory_notifier(migrate_on_reclaim_callback, MEMTIER_HOTPLUG_PRIO);
> +}

I suggest to call hotplug_memory_notifier() in memory_tier_init()
directly.  We are not working on demotion here.

> +
>  static int __init memory_tier_init(void)
>  {
>  	int node;
> @@ -96,6 +169,8 @@ static int __init memory_tier_init(void)
>  			node_property->perf_level = default_memtier_perf_level;
>  	}
>  	mutex_unlock(&memory_tier_lock);
> +
> +	migrate_on_reclaim_init();
>  	return 0;
>  }
>  subsys_initcall(memory_tier_init);

Best Regards,
Huang, Ying