linux-kernel - Re: [BUG] Description for memmap in kernel-parameters.txt is wrong

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Date:	Thu, 30 Jan 2014 12:26:22 -0800
From:	Randy Dunlap <rdunlap@...radead.org>
To:	Andiry Xu <andiry@...il.com>
CC:	linux-kernel@...r.kernel.org, Andiry Xu <andiry.xu@...il.com>,
	Linux MM <linux-mm@...ck.org>
Subject: Re: [BUG] Description for memmap in kernel-parameters.txt is wrong

On 01/30/2014 11:33 AM, Andiry Xu wrote:
> On Thu, Jan 30, 2014 at 11:25 AM, Randy Dunlap <rdunlap@...radead.org> wrote:
>> [adding linux-mm mailing list]
>>
>> On 01/30/2014 08:52 AM, Andiry Xu wrote:
>>> Hi,
>>>
>>> In kernel-parameters.txt, there is following description:
>>>
>>> memmap=nn[KMG]$ss[KMG]
>>>                         [KNL,ACPI] Mark specific memory as reserved.
>>>                         Region of memory to be used, from ss to ss+nn.
>>
>> Should be:
>>                           Region of memory to be reserved, from ss to ss+nn.
>>
>> but that doesn't help with the problem that you describe, does it?
>>
> 
> Actually it should be:
>                              Region of memory to be reserved, from nn to nn+ss.
> 
> That is, exchange nn and ss.

Yes, I understand that that's what you are reporting.  I just haven't yet
worked out how the code manages to exchange those 2 values.

>>
>>> Unfortunately this is incorrect. The meaning of nn and ss is reversed.
>>> For example:
>>>
>>> Command                  Expected                 Result
>>> memmap 2G$6G        6G - 8G reserved      2G - 8G reserved
>>> memmap 6G$2G        2G - 8G reserved      6G - 8G reserved
>>
>> Are you testing on x86?
>> The code in arch/x86/kernel/e820.c always parses mem_size followed by start address.
>> I don't (yet) see where it goes wrong...
>>
> 
> Yes, it's a x86 machine.
> 
>>
>>> Test kernel version 3.13, but I believe the issue has been there long ago.
>>>
>>> I'm not sure whether the description or implementation should be
>>> fixed, but apparently they do not match.
>>
>> I prefer to change the documentation and leave the implementation as is.
>>
> 
> That's fine. memmap itself works OK, it's just the description is
> wrong and people like me get confused.
> 
> Thanks,
> Andiry


-- 
~Randy
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