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

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Date:	Fri, 17 Dec 2010 12:06:23 -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 12:01 PM, Vivek Goyal wrote:
> On Fri, Dec 17, 2010 at 11:52:11AM -0800, Yinghai Lu wrote:
>> On 12/17/2010 11:50 AM, Vivek Goyal wrote:
>>> On Fri, Dec 17, 2010 at 11:46:08AM -0800, Yinghai Lu wrote:
>>>> On 12/17/2010 11:39 AM, H. Peter Anvin wrote:
>>>>> On 12/17/2010 10:21 AM, Yinghai Lu wrote:
>>>>>>>>
>>>>>>>> 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.
>>>>>>
>>>>>
>>>>> Why?  896 MiB is a 32-bit kernel limitation which doesn't have anything
>>>>> to do with the bzImage format.
>>>>>
>>>>> So unless there is something going on here, I suspect you're just plain
>>>>> flat wrong.
>>>>
>>>> kexec-tools have some checking when it loads bzImage.
>>>>
>>>
>>> Yinghai,
>>>
>>> I think x86_64 might have just inherited the settings of 32bit without
>>> giving it too much of thought. At that point of time nobody bothered
>>> to load the kernel from high addresses. So these might be artificial
>>> limits.
>>
>> good point.  will check that.
> 
> Yinghai,
> 
> On x86_64, I am not seeing "Crash kernel" entry in /proc/iomem.
> 
> I see following in dmesg.
> 
> "[    0.000000] Reserving 128MB of memory at 64MB for crashkernel (System
> RAM: 5120MB)"
> 
> Following is my /proc/iomem.
> 
> # cat /proc/iomem 
> 00000100-0000ffff : reserved
> 00010000-00096fff : System RAM
> 00097000-0009ffff : reserved
> 000c0000-000e7fff : pnp 00:0f
> 000e8000-000fffff : reserved
> 00100000-bffc283f : System RAM
>   01000000-015d1378 : Kernel code
>   015d1379-01aee00f : Kernel data
>   01bc8000-024b4c4f : Kernel bss
> bffc2840-bfffffff : reserved
> 
> So there is RAM available at the requested address still no entry for
> "Crash Kernel". This is both with 2.6.36 as well as 37-rc6 kernel. I am 
> wondering if insert_resource() is failing here?
> 

also could be memblock_x86_reserve() fail ...

Please check attached debug patch...

Thanks

	Yinghai

Download attachment "mb_debug.patches.tar.bz2" of type "application/x-bzip" (11774 bytes)