linux-kernel - Re: [tip:core/memblock] x86, memblock: Fix crashkernel allocation

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Date:	Thu, 7 Oct 2010 15:21:30 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"H. Peter Anvin" <h.peter.anvin@...el.com>
Cc:	"mingo@...hat.com" <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	"caiqian@...hat.com" <caiqian@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>,
	Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [tip:core/memblock] x86, memblock: Fix crashkernel allocation

On Thu, Oct 07, 2010 at 11:54:31AM -0700, H. Peter Anvin wrote:
> On 10/07/2010 11:18 AM, Vivek Goyal wrote:
> > 
> > Ok, I was browsing through kexec-tools, x86 bzImage code and trying to
> > refresh my memory what segments were being loaded and what were memory
> > address concerns.
> > 
> > - relocatable bzImage (max addr 0x37ffffff, 896MB). 
> > 	Though I don't know/understand where that 896MB come from.
> > 
> > - initrd (max addr 0x37ffffff, 896MB)
> > 	Don't know why 896MB as upper limit
> 
> 896 MB is presumably the (default!!) LOWMEM limit on 32 bits.  This is
> actually wrong if vmalloc= is also specified on command line, though, or
> with nonstandard compile-time options.
> 
> > - Purgatory (max addr 2G)
> > 
> > - A segment to keep elf headers (no limit)
> > 	These are accessed when second kernel as fully booted so can be
> > 	addressed in higher addresses.
> > 
> > - A backup segment to copy first 640K of memory (not aware of any limit)
> > - Setup/parameter segment (no limit)
> > 	- We don't really execute anything here and just access it for
> >   	  command line.
> 
> Probably has a 4 GB limit, since I believe it only has a 32-bit pointer.
> 
> > So atleast for bzImage it looks that if we specify crashkernel=128M<896M, it
> > will work.
> > 
> > So I am fine with above additional syntax for crashkernel=. May be we shall
> > have to the deprecate the crashkernel=X<@0 syntax.
> > 
> > CCing kexec list, in case others have any comments.
> 
> It would be easy enough to either deprecate or make it an alias for
> crashkernel=...<896M, which is basically what Yinghai's patch does.

Agreed.

So Yinghai's patch is fine. I need to write a patch for introducing
crashkernel=X<Y syntax to make the behavior explicit. Will do...

Thanks
Vivek
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