linux-kernel - Re: [PATCH 2/2] x86, e820 disable ACPI Memory Hotplug if memory mapping is specified by user [v2]

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Date:	Sun, 12 Jan 2014 18:46:42 -0500
From:	Prarit Bhargava <prarit@...hat.com>
To:	7eggert@....de
CC:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Len Brown <lenb@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linn Crosetto <linn@...com>, Pekka Enberg <penberg@...nel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Toshi Kani <toshi.kani@...com>,
	Tang Chen <tangchen@...fujitsu.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Vivek Goyal <vgoyal@...hat.com>, kosaki.motohiro@...il.com,
	dyoung@...hat.com, linux-acpi@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 2/2] x86, e820 disable ACPI Memory Hotplug if memory mapping
 is specified by user [v2]



On 01/11/2014 11:35 AM, 7eggert@....de wrote:
> 
> 
> On Fri, 10 Jan 2014, Prarit Bhargava wrote:
> 
>> kdump uses memmap=exactmap and mem=X values to configure the memory
>> mapping for the kdump kernel.  If memory is hotadded during the boot of
>> the kdump kernel it is possible that the page tables for the new memory
>> cause the kdump kernel to run out of memory.
>>
>> Since the user has specified a specific mapping ACPI Memory Hotplug should be
>> disabled in this case.
> 
> I'll ask just in case: Is it possible to want memory hotplug in spite of 
> using memmap=exactmap or mem=X?

Good question -- I can't think of a case.  When a user specifies "memmap" or
"mem" IMO they are asking for a very specific memory configuration.  Having
extra memory added above what the user has specified seems to defeat the purpose
of "memmap" and "mem".

P.
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