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Date:   Thu, 02 Nov 2023 11:17:44 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Li Zhijian <lizhijian@...itsu.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <rafael@...nel.org>, <linux-mm@...ck.org>, <y-goto@...itsu.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 1/4] drivers/base/node: Add demotion_nodes sys
 infterface

Li Zhijian <lizhijian@...itsu.com> writes:

> It shows the demotion target nodes of a node. Export this information to
> user directly.
>
> Below is an example where node0 node1 are DRAM, node3 is a PMEM node.
> - Before PMEM is online, no demotion_nodes for node0 and node1.
> $ cat /sys/devices/system/node/node0/demotion_nodes
>  <show nothing>
> - After node3 is online as kmem
> $ daxctl reconfigure-device --mode=system-ram --no-online dax0.0 && daxctl online-memory dax0.0
> [
>   {
>     "chardev":"dax0.0",
>     "size":1054867456,
>     "target_node":3,
>     "align":2097152,
>     "mode":"system-ram",
>     "online_memblocks":0,
>     "total_memblocks":7
>   }
> ]
> $ cat /sys/devices/system/node/node0/demotion_nodes
> 3
> $ cat /sys/devices/system/node/node1/demotion_nodes
> 3
> $ cat /sys/devices/system/node/node3/demotion_nodes
>  <show nothing>

We have /sys/devices/virtual/memory_tiering/memory_tier*/nodelist
already.  A node in a higher tier can demote to any node in the lower
tiers.  What's more need to be displayed in nodeX/demotion_nodes?

--
Best Regards,
Huang, Ying

> Signed-off-by: Li Zhijian <lizhijian@...itsu.com>
> ---
>  drivers/base/node.c          | 13 +++++++++++++
>  include/linux/memory-tiers.h |  6 ++++++
>  mm/memory-tiers.c            |  8 ++++++++
>  3 files changed, 27 insertions(+)
>
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 493d533f8375..27e8502548a7 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -7,6 +7,7 @@
>  #include <linux/init.h>
>  #include <linux/mm.h>
>  #include <linux/memory.h>
> +#include <linux/memory-tiers.h>
>  #include <linux/vmstat.h>
>  #include <linux/notifier.h>
>  #include <linux/node.h>
> @@ -569,11 +570,23 @@ static ssize_t node_read_distance(struct device *dev,
>  }
>  static DEVICE_ATTR(distance, 0444, node_read_distance, NULL);
>  
> +static ssize_t demotion_nodes_show(struct device *dev,
> +			     struct device_attribute *attr, char *buf)
> +{
> +	int ret;
> +	nodemask_t nmask = next_demotion_nodes(dev->id);
> +
> +	ret = sysfs_emit(buf, "%*pbl\n", nodemask_pr_args(&nmask));
> +	return ret;
> +}
> +static DEVICE_ATTR_RO(demotion_nodes);
> +
>  static struct attribute *node_dev_attrs[] = {
>  	&dev_attr_meminfo.attr,
>  	&dev_attr_numastat.attr,
>  	&dev_attr_distance.attr,
>  	&dev_attr_vmstat.attr,
> +	&dev_attr_demotion_nodes.attr,
>  	NULL
>  };
>  
> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> index 437441cdf78f..8eb04923f965 100644
> --- a/include/linux/memory-tiers.h
> +++ b/include/linux/memory-tiers.h
> @@ -38,6 +38,7 @@ void init_node_memory_type(int node, struct memory_dev_type *default_type);
>  void clear_node_memory_type(int node, struct memory_dev_type *memtype);
>  #ifdef CONFIG_MIGRATION
>  int next_demotion_node(int node);
> +nodemask_t next_demotion_nodes(int node);
>  void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
>  bool node_is_toptier(int node);
>  #else
> @@ -46,6 +47,11 @@ static inline int next_demotion_node(int node)
>  	return NUMA_NO_NODE;
>  }
>  
> +static inline next_demotion_nodes next_demotion_nodes(int node)
> +{
> +	return NODE_MASK_NONE;
> +}
> +
>  static inline void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)
>  {
>  	*targets = NODE_MASK_NONE;
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 37a4f59d9585..90047f37d98a 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -282,6 +282,14 @@ void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)
>  	rcu_read_unlock();
>  }
>  
> +nodemask_t next_demotion_nodes(int node)
> +{
> +	if (!node_demotion)
> +		return NODE_MASK_NONE;
> +
> +	return node_demotion[node].preferred;
> +}
> +
>  /**
>   * next_demotion_node() - Get the next node in the demotion path
>   * @node: The starting node to lookup the next node

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