linux-kernel - Re: [PATCH] memory hotplug: Correct page reservation checking

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Message-ID: <4E8B15D4.9080104@austin.ibm.com>
Date:	Tue, 04 Oct 2011 09:19:00 -0500
From:	Nathan Fontenot <nfont@...tin.ibm.com>
To:	Andrew Morton <akpm00@...il.com>
CC:	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	Greg KH <gregkh@...e.de>
Subject: Re: [PATCH] memory hotplug: Correct page reservation checking

On 10/03/2011 07:50 PM, Andrew Morton wrote:
> On Mon, 26 Sep 2011 10:22:33 -0500
> Nathan Fontenot <nfont@...tin.ibm.com> wrote:
> 
>> The check to ensure that pages of recently added memory sections are correctly
>> marked as reserved before trying to online the memory is broken.  The request
>> to online the memory fails with the following:
>>
>> kernel: section number XXX page number 256 not reserved, was it already online?
>>
>> This updates the page reservation checking to check the pages of each memory
>> section of the memory block being onlined individually.
> 
> Why was this only noticed now?  Is there something unusual about the
> way in which you're using it, or has nobody ever used this code, or...?
> 

As far as I know it is only the powerpc/pseries code that uses the feature that
allows memory blocks in sysfs to span multiple memory sections.  We do this
because on pseries memory add/remove is done on a per LMB basis and we can have
machine where an LMB spans multiple memory sections.

This was just noticed due to a lack of testing between the 2.6.38/39 kernels where
this feature originally went in and the current mainline kernel.

-Nathan

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