linux-kernel - Re: [PATCH v3 1/4] x86, kdump: Set crashkernel

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Message-ID: <51638A27.3040607@redhat.com>
Date:	Tue, 09 Apr 2013 11:25:27 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>, WANG Chao <chaowang@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/4] x86, kdump: Set crashkernel_low automatically

On 04/09/2013 02:37 AM, Yinghai Lu wrote:
> On Mon, Apr 8, 2013 at 12:09 AM, Dave Young <dyoung@...hat.com> wrote:
>>> We have now modified crashkernel=X to allocate memory beyong 4G (if
>>> available) and do not allocate low range for crashkernel if the user
>>> does not specify that with crashkernel_low=Y.  This causes regression
>>> if iommu is not enabled.  Without iommu, swiotlb needs to be setup in
>>> first 4G and there is no low memory available to second kernel.
>>
>> Is it possible to reuse the 1st kernel swiotlb region in 2nd capture
>> kernel if it's available?
> 
> If the first kernel is using intel iommu, and swiotlb is freed after intel
> iommus is enabled in first kernel.

Ok, also it's hard to handle such as 1st kernel iommu=off, 2nd kernel
iommu=on etc.

I have another question, under x86_64 consider 1st kernel memory < 4G,
is the swiotlb memory still necessary?

> 
>>
>>>
>>> Set crashkernel_low automatically if the user does not specify that.
>>>
>>> For system that does support IOMMU with kdump properly, user could
>>> specify crashkernel_low=0 to save that 72M low ram.
>>
>> How about make swiotlb size tunable in 1st kernel as well such as adding
>> a swiotlb_size= to cmdline, if it's set in 1st kernel crashkernel
>> reserving code can take it automaticlly.
>>
> can not understand this.

This maybe out of topic. I means swiotlb size is hardcoded, I'm thinking
how about make it configurable via kconfig or boot cmdline.

> 
> Thanks
> 
> Yinghai
> 


-- 
Thanks
Dave


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