Message-ID: <52D32962.5050908@redhat.com>
Date: Sun, 12 Jan 2014 18:46:42 -0500
From: Prarit Bhargava <prarit@redhat.com>
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To: 7eggert@gmx.de
CC: linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, Len Brown <lenb@kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>, Linn Crosetto <linn@hp.com>,
        Pekka Enberg <penberg@kernel.org>, Yinghai Lu <yinghai@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Toshi Kani <toshi.kani@hp.com>, Tang Chen <tangchen@cn.fujitsu.com>,
        Wen Congyang <wency@cn.fujitsu.com>, Vivek Goyal <vgoyal@redhat.com>,
        kosaki.motohiro@gmail.com, dyoung@redhat.com,
        linux-acpi@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 2/2] x86, e820 disable ACPI Memory Hotplug if memory mapping
 is specified by user [v2]
References: <1389380698-19361-1-git-send-email-prarit@redhat.com> <1389380698-19361-4-git-send-email-prarit@redhat.com> <alpine.DEB.2.02.1401111624170.20677@be1.lrz>
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On 01/11/2014 11:35 AM, 7eggert@gmx.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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