linux-kernel - Re: [PATCH] arm64: mm: Fix NOMAP page initialization

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Date:   Thu, 15 Dec 2016 11:01:04 +0800
From:   Yisheng Xie <xieyisheng1@...wei.com>
To:     Robert Richter <robert.richter@...ium.com>
CC:     Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        David Daney <david.daney@...ium.com>,
        "Mark Rutland" <mark.rutland@....com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        "James Morse" <james.morse@....com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        Hanjun Guo <guohanjun@...wei.com>,
        Xishi Qiu <qiuxishi@...wei.com>
Subject: Re: [PATCH] arm64: mm: Fix NOMAP page initialization

hi Robert,

On 2016/12/14 17:45, Robert Richter wrote:
> On 12.12.16 17:53:02, Yisheng Xie wrote:
>> It seems that memblock_is_memory() is also too strict for early_pfn_valid,
>> so what about this patch, which use common pfn_valid as early_pfn_valid
>> when CONFIG_HAVE_ARCH_PFN_VALID=y:
>> ------------
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index 0f088f3..9d596f3 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -1200,7 +1200,17 @@ static inline int pfn_present(unsigned long pfn)
>>  #define pfn_to_nid(pfn)                (0)
>>  #endif
>>
>> +#ifdef CONFIG_HAVE_ARCH_PFN_VALID
>> +static inline int early_pfn_valid(unsigned long pfn)
>> +{
>> +       if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
>> +               return 0;
>> +       return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
>> +}
> 
> I sent a V2 patch that uses pfn_present(). This only initilizes
> sections with memory.
hmm， maybe I do not quite catch what your mean, but I do not think
pfn_present is right for this case.

IMO, The valid_section() means the section with mem_map, not section with memory.

And:
    pfn_present
        -> present_section
which means the section is present but may not have mem_map, so it may not
have page struct at all for that section.

Please let me know, if I miss anything.

Thanks,
Yisheng Xie.


> 
> -Robert
> 
>> +#define early_pfn_valid early_pfn_valid
>> +#else
>>  #define early_pfn_valid(pfn)   pfn_valid(pfn)
>> +#endif
>>  void sparse_init(void);
>>  #else
>>  #define sparse_init()  do {} while (0)
>>
>>
>>
> 
>