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

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Message-ID: <CAOvWMLbs-sP+gJHV_5O6ZbV8eTpEKPVRVR238gFcPQeqhCjT3A@mail.gmail.com>
Date:	Thu, 30 Jan 2014 11:33:59 -0800
From:	Andiry Xu <andiry@...il.com>
To:	Randy Dunlap <rdunlap@...radead.org>
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 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.

>
>> 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
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