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

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Date:	Fri, 17 Dec 2010 15:01:39 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>
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 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?

Thanks
Vivek
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