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: <87sfm4gbat.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Wed, 10 Aug 2022 09:03:06 +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 v13 6/9] mm/demotion: Add pg_data_t member to track node
 memory tier details

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

> 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

I prefer "list_empty(memtype->tier_sibiling)".  But I will let you to
decide.

Best Regards,
Huang, Ying