linux-kernel - Re: [Patch v2 4/6] x86/mm: Refine debug print string retrieval function

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Date:   Fri, 6 Dec 2019 09:51:26 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, richard.weiyang@...il.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.or,
        tglx@...utronix.de
Subject: Re: [Patch v2 4/6] x86/mm: Refine debug print string retrieval
 function

On Thu, Dec 05, 2019 at 10:13:11AM +0100, Peter Zijlstra wrote:
>On Thu, Dec 05, 2019 at 10:14:01AM +0800, Wei Yang wrote:
>> Generally, the mapping page size are:
>> 
>>    4K, 2M, 1G
>> 
>> except in case 32-bit without PAE, the mapping page size are:
>> 
>>    4K, 4M
>> 
>> Based on PG_LEVEL_X definition and mr->page_size_mask, we can calculate
>> the mapping page size from a predefined string array.
>> 
>> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
>> ---
>>  arch/x86/mm/init.c | 39 +++++++++++++--------------------------
>>  1 file changed, 13 insertions(+), 26 deletions(-)
>> 
>> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
>> index 0eb5edb63fa2..ded58a31c679 100644
>> --- a/arch/x86/mm/init.c
>> +++ b/arch/x86/mm/init.c
>> @@ -308,29 +308,20 @@ static void __ref adjust_range_page_size_mask(struct map_range *mr,
>>  	}
>>  }
>>  
>> +static void __meminit mr_print(struct map_range *mr, unsigned int maxidx)
>>  {
>> +#if defined(CONFIG_X86_32) && !defined(CONFIG_X86_PAE)
>> +	static const char *sz[2] = { "4K", "4M" };
>> +#else
>> +	static const char *sz[4] = { "4K", "2M", "1G", "" };
>> +#endif
>> +	unsigned int idx, s;
>>  
>> +	for (idx = 0; idx < maxidx; idx++, mr++) {
>> +		s = (mr->page_size_mask >> PG_LEVEL_2M) & (ARRAY_SIZE(sz) - 1);
>
>Is it at all possible for !PAE to have 1G here, if you use the sz[4]
>definition unconditionally?
>

You mean remove the ifdef and use sz[4] for both condition?

Then how to differentiate 4M and 2M?

>> +		pr_debug(" [mem %#010lx-%#010lx] page size %s\n",
>> +			 mr->start, mr->end - 1, sz[s]);
>> +	}
>>  }

-- 
Wei Yang
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