linux-kernel - Re: [PATCH] x86, kdump: Set crashkernel

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Message-ID: <20130311150256.GC8482@redhat.com>
Date:	Mon, 11 Mar 2013 11:02:56 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>, WANG Chao <chaowang@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86, kdump: Set crashkernel_low automatically

On Mon, Mar 11, 2013 at 10:48:53AM -0400, Vivek Goyal wrote:
> On Sun, Mar 10, 2013 at 09:56:57PM -0700, Yinghai Lu wrote:
> > Current code does not set low range for crashkernel if the user
> > does not specify that.
> > 
> > That cause regressions on system that does not support intel_iommu
> > properly.
> > 
> > Chao said that his system does work well on 3.8 without extra parameter.
> > even iommu does not work with kdump.
> > 
> > Set crashkernel_low automatically if the user does not specify that.
> > 
> > For system that does support IOMMU with kdump properly, user could
> > specify crashkernel_low=0 to save that 72M low ram.
> > 
> 
> Hi Yinghai,
> 
> Had a question about crashkernel_auto_low. So this is the amount of
> memory rerved under 4G. I am not very clear about the semantics here.
> 
> So by default memory wil always come from areas above 4G (when
> crashkernel=X specified) and if user needs reserveation in lower memory
> area, it needs to be sepcified explicitly using crashkernel_low?
> 
> But will that not break the case of exising bzImage which are 32bit.
> They currently work if I specify crashkernel=256M. Now suddenly memory
> will come from higher addresses and 32bit bzImage can't be loaded there.
> Or I understood the syntax part wrong.
> 

IOW, wouldn't it be better that crashkernel=X first tries to find
requested amount of memory in lowest memory area available/possible.

Thanks
Vivek
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