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

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Message-ID: <20101217180242.GB12425@redhat.com>
Date:	Fri, 17 Dec 2010 13:02:42 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Yinghai <yinghai@...nel.org>,
	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 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.


>I'm assuming that the usage of a 32-bit kdump kernel for a 64-bit main
> kernel is nonexistent.

In the past I have run into 1-2 folks who were using 32bit kdump kernel
on 64bit main. But again for those, the workaround is to specify the
different crashkernel= syntax and explicityly specify where to reserve
memory.

Thanks
Vivek
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