linux-kernel - Re: [Fastboot] Stupid kexec/kdump question...

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Message-ID: <20060927131123.GA2514@in.ibm.com>
Date:	Wed, 27 Sep 2006 09:11:23 -0400
From:	Vivek Goyal <vgoyal@...ibm.com>
To:	Valdis.Kletnieks@...edu
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...l.org>, fastboot@...ts.osdl.org,
	linux-kernel@...r.kernel.org
Subject: Re: [Fastboot] Stupid kexec/kdump question...

On Wed, Sep 27, 2006 at 08:51:50AM -0400, Valdis.Kletnieks@...edu wrote:
> On Wed, 27 Sep 2006 02:00:07 MDT, Eric W. Biederman said:
[..]
> > At that level I would say that below 32M is where you start dealing with
> > custom built programs, instead of slapping a bunch of utilities inside
> > a ramdisk.  I suspect with a little care you could get a few K user
> > space executable and fit everything inside of 4M.  But I don't know if anyone
> > is that ambitious yet.
> 
> Well, the stripped down kernel is right around 2M.  Unfortunately, I need
> to run lvm.static, which is another 1.5M at least.  So unless busybox has
> grown support for LVM, I'm looking at 8M at best.
> 
> Another stupid question - I see how the first kernel gets the 'crashkernel='
> parameter and knows how much space there is.  But if you set it to 32M@16M,
> how does the kdump kernel know it only has 32M?  Or does it just start at
> the 16M line, and it's your job to make sure it doesn't go over the 48M line
> and start corrupting the dump?
> 

Kdump kernel is booted with User defined memory map. For this purpose
kexec-tools passes memmap=exactmap option on command line to the second
kernel. Hence second kernel execution is bounded within reserved memory
region.

-Vivek
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