linux-kernel - Re: [PATCH 1/2 v2] x86: add max

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Date:	Tue, 12 Jun 2012 14:26:09 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	rob@...dley.net, tglx@...utronix.de,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	bhelgaas@...gle.com
Subject: Re: [PATCH 1/2 v2] x86: add max_addr boot option

At 06/12/2012 05:15 AM, H. Peter Anvin Wrote:
> On 06/11/2012 01:44 AM, Wen Congyang wrote:
>> Currently, the boot option max_addr is only supported on ia64 platform.
>> We also need it on x86 platform.
>> For example:
>> There are two nodes:
>>  NODE#0  address range 0x00000000 00000000 - 0x00010000 00000000
>>  NODE#1  address range 0x00010000 00000000 - 0x00020000 00000000
>> If we only want to use node0, we can specify the max_addr. The boot
>> option "mem=" can do the same thing now. But the boot option "mem="
>> means the total memory used by the system. If we tell the user
>> that the boot option "mem=" can do this, it will confuse the user.
>> So we need an new boot option "max_addr" on x86 platform.
>>
> 
> I fail to see what this does that cannot be done with the
> since-long-existing memmap= option.  Could you address why memmap=
> doesn't match your needs?

The memmap= option is very diffcult to use. The end user should know the memory
map in the system. The end user can get the max address of NODE#0, but he
may not know the memory map for NODE#0. If the end user give the wrong memory
map, the kernel can not boot. For example: I add memmap=16G@0 in the kernel
parameter, and the kernel cannot boot. The max_addr is more easier to use.

Thanks
Wen Congyang

> 
> 	-hpa
> 
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