linux-kernel - Re: kdump broken on 2.6.37-rc4

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Message-ID: <4D0BAA24.3080801@kernel.org>
Date:	Fri, 17 Dec 2010 10:21:24 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Maxim Uvarov <muvarov@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Neil Horman <nhorman@...hat.com>
Subject: Re: kdump broken on 2.6.37-rc4

On 12/17/2010 10:02 AM, Vivek Goyal wrote:
> On Fri, Dec 17, 2010 at 09:56:42AM -0800, H. Peter Anvin wrote:
>> On 12/17/2010 09:01 AM, Vivek Goyal wrote:
>>> On Thu, Dec 16, 2010 at 07:58:48PM -0800, Yinghai wrote:
>>>> Please don't do that to 64 bit
>>>>
>>>> My big system with 1024g memory and a lot of cards with rhel 6 to make kdump work must have crashkernel=512m and second kernel need to take pci=nomsi
>>>>
>>>
>>> I agree here that we should not do it for 64 bit.
>>>
>>> - Just because we need it for 32 bit does not mean we should limit it for
>>>   64bit. And we do want to have the capability to boot the kernel from as
>>>   high memory as possible so creating another aritificial limit is counter
>>>   to that.
>>>
>>> - I would not worry too much about backward compatibility and allow
>>>   booting 32bit kernel till 768MB. The reason being that most of the
>>>   distros use same kernel for crash dumping as regular kernel. Maintainig
>>>   two separate kernels is big hassle.
>>>
>>>   So a small set of people who run into issue, would need to change kernel
>>>   command line "crashkernel=128M@64M" or something similar.
>>>
>>
>> Do we have actual testing for how high the 64-bit kernel will load?
> 
> I will do some experiments on my box today and let you know.

if bzImage is used, it is 896M.

or crashkernel=... will take two ranges like one high and one low.

also kexec bzImage in 64bit should use startup_64 aka 0x200 offset instead of startup_32 in arch/x86/boot/compressed/head_64.S

then bzImage can be put above 4G...

Thanks

Yinghai
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