On Thu, Jan 30, 2014 at 11:25 AM, Randy Dunlap <rdunlap@xxxxxxxxxxxxx> 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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