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Subject: Re: [PATCH] mm/sparse: use __nr_to_section(section_nr) to get
 mem_section
To:     Wei Yang <richardw.yang@linux.intel.com>,
        akpm@linux-foundation.org, osalvador@suse.de,
        pasha.tatashin@oracle.com, mhocko@suse.com
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20190809010242.29797-1-richardw.yang@linux.intel.com>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <e17278f0-94dc-e0c6-379b-b7694cec3247@arm.com>
Date:   Fri, 9 Aug 2019 14:39:59 +0530
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On 08/09/2019 06:32 AM, Wei Yang wrote:
> __pfn_to_section is defined as __nr_to_section(pfn_to_section_nr(pfn)).

Right.

> 
> Since we already get section_nr, it is not necessary to get mem_section
> from start_pfn. By doing so, we reduce one redundant operation.
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>

Looks right.

With this applied, memory hot add still works on arm64.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

> ---
>  mm/sparse.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 72f010d9bff5..95158a148cd1 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -867,7 +867,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>  	 */
>  	page_init_poison(pfn_to_page(start_pfn), sizeof(struct page) * nr_pages);
>  
> -	ms = __pfn_to_section(start_pfn);
> +	ms = __nr_to_section(section_nr);
>  	set_section_nid(section_nr, nid);
>  	section_mark_present(ms);
>  
>