linux-kernel - Re: [PATCH v3] mm: hugetlb: eliminate memory-less nodes handling

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Date:   Tue, 13 Sep 2022 17:57:15 +0800
From:   Muchun Song <muchun.song@...ux.dev>
To:     David Hildenbrand <david@...hat.com>
Cc:     Muchun Song <songmuchun@...edance.com>,
        Greg KH <gregkh@...uxfoundation.org>, rafael@...nel.org,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>, ying.huang@...el.com,
        aneesh.kumar@...ux.ibm.com, David Rientjes <rientjes@...gle.com>,
        linux-kernel@...r.kernel.org, Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH v3] mm: hugetlb: eliminate memory-less nodes handling



> On Sep 8, 2022, at 20:21, David Hildenbrand <david@...hat.com> wrote:
> 
> On 08.09.22 09:58, Muchun Song wrote:
>> The memory-notify-based approach aims to handle meory-less nodes, however, it just adds
>> the complexity of code as pointed by David in thread [1].  The handling of memory-less
>> nodes is introduced by commit 4faf8d950ec4 ("hugetlb: handle memory hot-plug events").
>> From its commit message, we cannot find any necessity of handling this case. So, we can
>> simply register/unregister sysfs entries in register_node/unregister_node to simlify the
>> code.
>> BTW, hotplug callback added because in hugetlb_register_all_nodes() we register sysfs
>> nodes only for N_MEMORY nodes, seeing commit 9b5e5d0fdc91, which said it was a preparation
>> for handling memory-less nodes via memory hotplug. Since we want to remove memory hotplug,
>> so make sure we only register per-node sysfs for online (N_ONLINE) nodes in
>> hugetlb_register_all_nodes().
>> https://lore.kernel.org/linux-mm/60933ffc-b850-976c-78a0-0ee6e0ea9ef0@redhat.com/ [1]
>> Suggested-by: David Hildenbrand <david@...hat.com>
>> Signed-off-by: Muchun Song <songmuchun@...edance.com>
>> ---
>> v3:
>>  - Fix 'struct node' is not declared reported by LTP.
>> v2:
>>  - Move declaration of function related to hugetlb to hugetlb.h (David).
>>  - Introduce hugetlb_sysfs_initialized() and call it from hugetlb_sysfs_init() (David).
>>  - Move hugetlb_register_all_nodes() into hugetlb_sysfs_init() (David).
>>  - Fix implicit-function-declaration reported by LKP.
>>  - Register per-node sysfs for online (N_ONLINE) nodes instead of N_MEMORY (Aneesh).
>>  drivers/base/node.c     |  8 +++--
>>  include/linux/hugetlb.h | 14 +++++++++
>>  mm/hugetlb.c            | 81 ++++++++++++++++++++++---------------------------
>>  3 files changed, 57 insertions(+), 46 deletions(-)
> 
> 
> 
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -3880,24 +3880,14 @@ static int hugetlb_sysfs_add_hstate(struct hstate *h, struct kobject *parent,
>>  	return 0;
>>  }
>>  -static void __init hugetlb_sysfs_init(void)
>> -{
>> -	struct hstate *h;
>> -	int err;
>> -
>> -	hugepages_kobj = kobject_create_and_add("hugepages", mm_kobj);
>> -	if (!hugepages_kobj)
>> -		return;
>> +#ifdef CONFIG_NUMA
>> +static bool hugetlb_sysfs_initialized __ro_after_init;
>>  -	for_each_hstate(h) {
>> -		err = hugetlb_sysfs_add_hstate(h, hugepages_kobj,
>> -					 hstate_kobjs, &hstate_attr_group);
>> -		if (err)
>> -			pr_err("HugeTLB: Unable to add hstate %s", h->name);
>> -	}
>> +static inline void hugetlb_mark_sysfs_initialized(void)
>> +{
>> +	hugetlb_sysfs_initialized = true;
>>  }
> 
> Do we really need a separate function for this? Why not simply always set that from hugetlb_sysfs_init() ?

I can remove this helper.

> 
> I'm also not sure if we really want to optimize out one variable for !CONFIG_NUMA.

Either is fine to me. I think the optimization does not bring any complexity.
So I’ll keep it the same in the next version unless anyone is against this.

> 
> Anyhow, in general
> 
> Acked-by: David Hildenbrand <david@...hat.com>

Thanks David.

> 
> 
> -- 
> Thanks,
> 
> David / dhildenb
>