Re: [PATCH v6 09/13] mm/demotion: Add pg_data_t member to track node memory tier details

From: Ying Huang <ying.huang@intel.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
	linux-mm@kvack.org, akpm@linux-foundation.org
Cc: Wei Xu <weixugc@google.com>, Greg Thelen <gthelen@google.com>,
	Yang Shi <shy828301@gmail.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Tim C Chen <tim.c.chen@intel.com>,
	Brice Goglin <brice.goglin@gmail.com>,
	Michal Hocko <mhocko@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Hesham Almatary <hesham.almatary@huawei.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Alistair Popple <apopple@nvidia.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Feng Tang <feng.tang@intel.com>,
	Jagdish Gediya <jvgediya@linux.ibm.com>,
	Baolin Wang <baolin.wang@linux.alibaba.com>,
	David Rientjes <rientjes@google.com>
Subject: Re: [PATCH v6 09/13] mm/demotion: Add pg_data_t member to track node memory tier details
Date: Mon, 13 Jun 2022 15:07:57 +0800	[thread overview]
Message-ID: <d4170cd543b250260678341c3ffbe5bb8aaf97f1.camel@intel.com> (raw)
In-Reply-To: <20220610135229.182859-10-aneesh.kumar@linux.ibm.com>

On Fri, 2022-06-10 at 19:22 +0530, Aneesh Kumar K.V wrote:
> Also update different helpes to use NODE_DATA()->memtier. Since
> node specific memtier can change based on the reassignment of
> NUMA node to a different memory tiers, accessing NODE_DATA()->memtier
> needs to under an rcu read lock of memory_tier_lock.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>  include/linux/memory-tiers.h |  14 +++++
>  include/linux/mmzone.h       |   3 ++
>  mm/memory-tiers.c            | 102 ++++++++++++++++++++++++++---------
>  3 files changed, 94 insertions(+), 25 deletions(-)
> 
> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> index 52896f5970b7..53f3e4c7cba8 100644
> --- a/include/linux/memory-tiers.h
> +++ b/include/linux/memory-tiers.h
> @@ -6,6 +6,9 @@
>  
> 
>  #ifdef CONFIG_TIERED_MEMORY
>  
> 
> +#include <linux/device.h>
> +#include <linux/nodemask.h>
> +
>  #define MEMORY_TIER_HBM_GPU	0
>  #define MEMORY_TIER_DRAM	1
>  #define MEMORY_TIER_PMEM	2
> @@ -18,13 +21,24 @@
>  #define MAX_STATIC_MEMORY_TIERS  3
>  #define MAX_MEMORY_TIERS  (MAX_STATIC_MEMORY_TIERS + 2)
>  
> 
> +struct memory_tier {
> +	struct list_head list;
> +	struct device dev;
> +	nodemask_t nodelist;
> +	int rank;
> +};
> +

I suggest to use two data structure,

struct memory_tier {
	struct list_head list;
	nodemask_t nodelist;
	int rank;
};

struct memory_tier_dev {
	struct list_head list;
	struct device dev;
	struct memory_tier *tier;
};

Then we can put struct memory_tier here and still hide struct
memory_tier_dev in memory_tiers.c.  In this way, we don't need to
force all struct memory_tier users to compile the entire driver core
headers.  And we can separate the user space interface implementation
from the other part of the kernel.

>  extern bool numa_demotion_enabled;
>  int node_create_and_set_memory_tier(int node, int tier);
>  int next_demotion_node(int node);
>  int node_set_memory_tier(int node, int tier);
>  int node_get_memory_tier_id(int node);
>  int node_reset_memory_tier(int node, int tier);
> +struct memory_tier *node_get_memory_tier(int node);
> +void node_put_memory_tier(struct memory_tier *memtier);

I don't find caller of these 2 functions in series.  Can we remove
these functions?

Best Regards,
Huang, Ying

[snip]