linux-kernel - Re: [PATCH 0/8] v5 De-couple sysfs memory directories from memory sections

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Date:	Thu, 02 Sep 2010 12:39:47 -0500
From:	Nathan Fontenot <nfont@...tin.ibm.com>
To:	Anton Blanchard <anton@...ba.org>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linuxppc-dev@...abs.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Greg KH <greg@...ah.com>, akpm@...ux-foundation.org
Subject: Re: [PATCH 0/8] v5 De-couple sysfs memory directories from memory
 sections

On 08/31/2010 04:57 PM, Anton Blanchard wrote:
> 
> Hi Nathan,
> 
>> This set of patches de-couples the idea that there is a single
>> directory in sysfs for each memory section.  The intent of the
>> patches is to reduce the number of sysfs directories created to
>> resolve a boot-time performance issue.  On very large systems
>> boot time are getting very long (as seen on powerpc hardware)
>> due to the enormous number of sysfs directories being created.
>> On a system with 1 TB of memory we create ~63,000 directories.
>> For even larger systems boot times are being measured in hours.
>>
>> This set of patches allows for each directory created in sysfs
>> to cover more than one memory section.  The default behavior for
>> sysfs directory creation is the same, in that each directory
>> represents a single memory section.  A new file 'end_phys_index'
>> in each directory contains the physical_id of the last memory
>> section covered by the directory so that users can easily
>> determine the memory section range of a directory.
> 
> I tested this on a POWER7 with 2TB memory and the boot time improved from
> greater than 6 hours (I gave up), to under 5 minutes. Nice!

Thanks for testing this out.  I was able to test this on a 1 TB system
and saw memory sysfs creation times go from 10 minutes to a few seconds.
It's good to see the difference for a 2 TB system.

-Nathan

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