linux-kernel - Re: [PATCH v13 6/9] mm/demotion: Add pg_data_t member to track node memory tier details

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Message-ID: <f3590060-3b7b-e576-0742-bd0dae8c760d@linux.ibm.com>
Date:   Tue, 9 Aug 2022 11:11:15 +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 v13 6/9] mm/demotion: Add pg_data_t member to track node
 memory tier details

On 8/9/22 10:51 AM, Huang, Ying wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> writes:
> 
>> 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 happen under an rcu read lock or memory_tier_lock.
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
>> ---
>>  include/linux/mmzone.h |  3 +++
>>  mm/memory-tiers.c      | 38 ++++++++++++++++++++++++++++++++------
>>  2 files changed, 35 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index aab70355d64f..353812495a70 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -928,6 +928,9 @@ typedef struct pglist_data {
>>  	/* Per-node vmstats */
>>  	struct per_cpu_nodestat __percpu *per_cpu_nodestats;
>>  	atomic_long_t		vm_stat[NR_VM_NODE_STAT_ITEMS];
>> +#ifdef CONFIG_NUMA
>> +	struct memory_tier __rcu *memtier;
>> +#endif
>>  } pg_data_t;
>>  
>>  #define node_present_pages(nid)	(NODE_DATA(nid)->node_present_pages)
>> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
>> index 02e514e87d5c..3778ac6a44a1 100644
>> --- a/mm/memory-tiers.c
>> +++ b/mm/memory-tiers.c
>> @@ -5,6 +5,7 @@
>>  #include <linux/kobject.h>
>>  #include <linux/memory.h>
>>  #include <linux/random.h>
>> +#include <linux/mmzone.h>
>>  #include <linux/memory-tiers.h>
>>  
>>  #include "internal.h"
>> @@ -137,12 +138,18 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty
>>  
>>  static struct memory_tier *__node_get_memory_tier(int node)
>>  {
>> -	struct memory_dev_type *memtype;
>> +	pg_data_t *pgdat;
>>  
>> -	memtype = node_memory_types[node];
>> -	if (memtype && node_isset(node, memtype->nodes))
>> -		return memtype->memtier;
>> -	return NULL;
> 
> After adding pgdat->memtier, it appears there's unnecessary to keep
> memtype->memtier?
> 

It do simplify find_create_memory_tier() where I use if (memtype->memtier) 
to check whether the memtype is already added to a memory tier. I could switch
that to list_empty(memtype->tier_sibiling). But I felt the current one is much
cleaner
.
-aneesh