linux-kernel - Re: [PATCH] x86, kdump: Set crashkernel

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Date:	Mon, 18 Mar 2013 14:14:28 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	Yinghai Lu <yinghai@...nel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	WANG Chao <chaowang@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86, kdump: Set crashkernel_low automatically

On 03/18/2013 01:00 PM, Vivek Goyal wrote:
> On Mon, Mar 18, 2013 at 12:10:47PM -0700, H. Peter Anvin wrote:
>> On 03/18/2013 08:33 AM, Vivek Goyal wrote:
>>>
>>> Thinking more about it, if ongoing DMA is an issue, then setting up
>>> software iotlb in those areas is also prone to being overwritten by
>>> those DMAs. Hence, reserving memory low where no DMA is setup by first
>>> kernel, seems somewhat safer.
>>>
>>
>> Agreed.  We really should reserve some memory low.
> 
> So which approach do you like for reserving some memory low.
> 
> - User specifies crashkernel_low=X to reserve some memory. Biggest problem
>   here is how does user know how much memory is required for setting up
>   swiotlb.
> 
> - Take yinghai's patch where by default low memory for swiotlb is reserved
>   and a user need to opt out of it using crashkernel_low=0 if system has
>   iommu enabled.
> 
> - crashkernel=X by default first looks for specified memory in low
>   memory area.
> 
> I kind of like yinghai's approach. It is little wasteful of memory when
> memory is reserved high but atleast user does not have know how much memory
> to reserve low it works both when memory is reserved low (system does
> not have any RAM mapped above 4G) and when memory is reserved high.
> 

I would agree, I think it is the most user friendly.

	-hpa


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