linux-kernel - Re: [PATCH 2/3] mm/sparsemem: get physical address to page struct instead of virtual address to pfn

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Date:   Fri, 7 Feb 2020 10:53:14 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        akpm@...ux-foundation.org, osalvador@...e.de,
        dan.j.williams@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, david@...hat.com
Subject: Re: [PATCH 2/3] mm/sparsemem: get physical address to page struct
 instead of virtual address to pfn

On Fri, Feb 07, 2020 at 12:11:34PM +0800, Baoquan He wrote:
>On 02/07/20 at 07:16am, Wei Yang wrote:
>> memmap should be the physical address to page struct instead of virtual
>> address to pfn.
>
>Maybe not, memmap stores a virtual address.
>
>> 
>> Since we call this only for SPARSEMEM_VMEMMAP, pfn_to_page() is valid at
>> this point.
>> 
>> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
>> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
>> CC: Dan Williams <dan.j.williams@...el.com>
>> ---
>>  mm/sparse.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/mm/sparse.c b/mm/sparse.c
>> index b5da121bdd6e..56816f653588 100644
>> --- a/mm/sparse.c
>> +++ b/mm/sparse.c
>> @@ -888,7 +888,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>>  	/* Align memmap to section boundary in the subsection case */
>>  	if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) &&
>>  		section_nr_to_pfn(section_nr) != start_pfn)
>> -		memmap = pfn_to_kaddr(section_nr_to_pfn(section_nr));
>> +		memmap = pfn_to_page(section_nr_to_pfn(section_nr));
>
>With Dan's confirmation, sub-section is only valid in vmemmap case. I
>think the old if (section_nr_to_pfn(section_nr) != start_pfn) is enough
>to filter out non vmemmap case. So only below code is good:
>
> +		memmap = pfn_to_page(section_nr_to_pfn(section_nr));
>

You mean replace pfn_to_kaddr with pfn_to_page ?

>>  	sparse_init_one_section(ms, section_nr, memmap, ms->usage, 0);
>>  
>>  	return 0;
>> -- 
>> 2.17.1
>> 

-- 
Wei Yang
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