linux-kernel - RE: [Patch 4/8] ia64: implement crashkernel=auto

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Message-ID: <A6AD88C3F2289247BE726C37303E1EB8B954B3BB@orsmsx505.amr.corp.intel.com>
Date:	Fri, 28 Aug 2009 13:08:30 -0700
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	'Amerigo Wang' <amwang@...hat.com>
CC:	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	'Anton Vorontsov' <avorontsov@...mvista.com>,
	"Luck, Tony" <tony.luck@...el.com>,
	"'linux-ia64@...r.kernel.org'" <linux-ia64@...r.kernel.org>,
	'Neil Horman' <nhorman@...hat.com>,
	"'Eric W. Biederman'" <ebiederm@...ssion.com>,
	"'kamezawa.hiroyu@...fujitsu.com'" <kamezawa.hiroyu@...fujitsu.com>,
	'Andi Kleen' <andi@...stfloor.org>,
	'Michael Ellerman' <michael@...erman.id.au>,
	"'M. Mohan Kumar'" <mohan@...ibm.com>,
	"'akpm@...ux-foundation.org'" <akpm@...ux-foundation.org>,
	"'bernhard.walle@....de'" <bernhard.walle@....de>,
	'Ingo Molnar' <mingo@...e.hu>
Subject: RE: [Patch 4/8] ia64: implement crashkernel=auto

>>>>> +	unsigned long long ret;
>>>>> +
>>>>> +	if (total_size >= GBYTES(4) && total_size < GBYTES(12))
>>>>> +		ret = MBYTES(256);
>>>>> +	else if (total_size >= GBYTES(12) && total_size < GBYTES(128))
>>>>> +		ret = MBYTES(512);
>>>>> +	else if (total_size >= GBYTES(128) && total_size < GBYTES(256))
>>>>> +		ret = MBYTES(768);
>>>>> +	else if (total_size >= GBYTES(256) && total_size < GBYTES(378))
>>>>> +		ret = MBYTES(1024);
>>>>> +	else if (total_size >= GBYTES(318) && total_size < GBYTES(512))
>>>>> +		ret = MBYTES(1536);
>>>>> +	else if (total_size >= GBYTES(512) && total_size < GBYTES(768))
>>>>> +		ret = MBYTES(2048);
>>>>> +	else
>>>>> +		ret = MBYTES(3072);
>>>>> +	if (!ia64_platform_is("sn2") && !ia64_platform_is("uv"))
>>>>> +		if (ret > GBYTES(4))
>>>>> +			ret = ret / GBYTES(4) * MBYTES(256);
>>>>>
>>>>>
>>>> This code doesn't make sense to me. What you really want is following
>>>>
>>> code, right?
>>>
>>>> +		if (total_size > GBYTES(4))
>>>> +			ret = total_size / GBYTES(4) * MBYTEST(256)
>>>>
>>>>
>>>>
>>> Nope. Check check_crashkernel_memory().
>>>
>>
>> This statement will be ALWAYS false:
>> +		if (ret > GBYTES(4))
>> since ret's max value is 3GB after the above total_size checks.
>>
>> So the code doesn't make sense. Did I miss something?
>>
>
>Oops, in fact it was supposed to be:
>
>  if (ret + base > GBYTES(4))
>    //blah blah
>
>Hmm, but is it possible for ia64 to choose a base address above 1G? If
>no, that code can be removed.

I think you don't need to consider the base here. This arch_default_crash_size() only returns size. Later on, ia64 setup_crashkernel() will find a base value in reserved region and check if the base value is under 4GB etc.

Thanks.

-Fenghua
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