linux-kernel - Re: [RESEND][PATCH v2 2/2] powerpc/fadump: parse fadump reserve memory size based on memory range

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Date:	Mon, 8 Aug 2016 13:45:50 +0530
From:	Hari Bathini <hbathini@...ux.vnet.ibm.com>
To:	Michael Ellerman <mpe@...erman.id.au>, rusty@...tcorp.com.au,
	ebiederm@...ssion.com, vgoyal@...hat.com,
	linuxppc-dev <linuxppc-dev@...abs.org>
Cc:	Mahesh J Salgaonkar <mahesh@...ux.vnet.ibm.com>,
	kexec@...ts.infradead.org, lkml <linux-kernel@...r.kernel.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: [RESEND][PATCH v2 2/2] powerpc/fadump: parse fadump reserve
 memory size based on memory range



On Friday 05 August 2016 12:23 AM, Hari Bathini wrote:
>
> On Thursday 04 August 2016 03:15 PM, Michael Ellerman wrote:
>> Hari Bathini <hbathini@...ux.vnet.ibm.com> writes:
>> ...
>>>   /**
>>>    * fadump_calculate_reserve_size(): reserve variable boot area 5% 
>>> of System RAM
>>>    *
>>> @@ -212,12 +262,17 @@ static inline unsigned long 
>>> fadump_calculate_reserve_size(void)
>>>   {
>>>       unsigned long size;
>>>   +    /* sets fw_dump.reserve_bootvar */
>>> +    parse_fadump_reserve_mem();
>>> +
>>>       /*
>>>        * Check if the size is specified through fadump_reserve_mem= 
>>> cmdline
>>>        * option. If yes, then use that.
>>>        */
>>>       if (fw_dump.reserve_bootvar)
>>>           return fw_dump.reserve_bootvar;
>>> +    else
>>> +        printk(KERN_INFO "fadump: calculating default boot size\n");
>>>         /* divide by 20 to get 5% of value */
>>>       size = memblock_end_of_DRAM() / 20;
>> The code already knows how to reserve 5% based on the size of the 
>> machine's
>> memory, as long as no commandline parameter is passed. So why can't we
>> just use that logic?
>
> Hi Michael,
>
> That is the default value reserved but not a good enough value for
> every case. It is a bit difficult to come up with a robust formula
> that works for every case as new kernel changes could make the
> values obsolete. But it won't be all that difficult to find values that
> work for different memory ranges for a given kernel version.
> Passing that as range based input with "fadump_reserve_mem"
> parameter would work for every memory configuration on a
> given system, which is what this patch is trying to provide..
>

Hi Michael,

You want me to add this to the changelog on respin?

Thanks
Hari

> Thanks
> Hari
>
>
>> cheers
>>
>