linux-kernel - Re: [PATCH] memory hotplug disable boot option

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Message-ID: <4C24C96F.4030709@austin.ibm.com>
Date:	Fri, 25 Jun 2010 10:21:19 -0500
From:	Nathan Fontenot <nfont@...tin.ibm.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memory hotplug disable boot option

On 06/25/2010 09:56 AM, Andi Kleen wrote:
> On Fri, Jun 25, 2010 at 09:51:37AM -0500, Nathan Fontenot wrote:
>>>
>>>>> Proposed patch to disable memory hotplug via a boot option,
>>>>> mem_hotplug=[on|off].  The patch only disables memory hotplug in that it 
>>>>> prevents the creation of the memory sysfs directories for memory sections.
>>>>>
>>>>> This patch is meant to help alleviate very long boot times on systems with
>>>>> large memory (1+ TB) and many memory sections (10's of thousands).
>>>>
>>>> Why making simple /sys file is so slowly? Couldn't we fix such performance
>>>> problem?
>>
>> The issue is the large number of sysfs memory directories that get created.
>> On a system with 1 TB of memory I am seeing ~63,00 directories.  The long
> 
> Maybe you could simply make the memory blocks larger on such large systems?
> I agree 6k blocks are probably not very useful, but maybe 10 or 100 are?
> 

Yes, this would work to reduce the number of memory sections created.  The reason
I have not gone this route is that increasing the memory section size would
break DLPAR memory add and remove for powerpc pseries.

-Nathan
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