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

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Date:	Mon, 11 Mar 2013 11:55:52 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Vivek Goyal <vgoyal@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	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 03/11/2013 11:50 AM, Yinghai Lu wrote:
>>
>> What is the purpose of reserving that kind of memory below 896 MB?  If
>> you have a 32-bit system, it will likely be useless since you are
>> robbing the primary of most of lowmem, on a 64-bit system 896 MB is not
>> a magic value in any way...?
> 
> We did not touch 32 bit system.
> 
> Do you mean that we should
> For 64bit, we should try under 4G, and then try MAXMEM
> instead of try under 896M, then 4G, and MAXMEM?
> 
> Try 896M at first, we will let user to avoid updating their kexec-tools.
> 

Are you saying 896M is somehow hardcoded into kexec-tools?

I actually disagree with trying low memory at all.  Push kdump as high
into the memory range as we can go, if there is a performance penalty it
is much better to take it in the kdump kernel.

All the voodoo to try to keep people from updating kexec-tools is
disturbing; although breaking userspace is bad, updating kexec-tools is
probably easier than updating the kernel, and carrying the voodoo on
indefinitely has serious consequences.

	-hpa


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