Date: Wed, 14 Aug 2013 12:40:43 -0700
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: Dave Hansen <dave@sr71.net>, Nathan Fontenot <nfont@linux.vnet.ibm.com>,
        Cody P Schafer <cody@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Lai Jiangshan <laijs@cn.fujitsu.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [RFC][PATCH] drivers: base: dynamic memory block creation
Message-ID: <20130814194043.GA10469@kroah.com>
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On Wed, Aug 14, 2013 at 02:31:45PM -0500, Seth Jennings wrote:
> Large memory systems (~1TB or more) experience boot delays on the order
> of minutes due to the initializing the memory configuration part of
> sysfs at /sys/devices/system/memory/.
> 
> ppc64 has a normal memory block size of 256M (however sometimes as low
> as 16M depending on the system LMB size), and (I think) x86 is 128M.  With
> 1TB of RAM and a 256M block size, that's 4k memory blocks with 20 sysfs
> entries per block that's around 80k items that need be created at boot
> time in sysfs.  Some systems go up to 16TB where the issue is even more
> severe.
> 
> This patch provides a means by which users can prevent the creation of
> the memory block attributes at boot time, yet still dynamically create
> them if they are needed.
> 
> This patch creates a new boot parameter, "largememory" that will prevent
> memory_dev_init() from creating all of the memory block sysfs attributes
> at boot time.  Instead, a new root attribute "show" will allow
> the dynamic creation of the memory block devices.
> Another new root attribute "present" shows the memory blocks present in
> the system; the valid inputs for the "show" attribute.

Ick, no new boot parameters please, that's just a mess for distros and
users.

How about tying this into the work that has been happening on lkml with
booting large-memory systems faster?  The work there should solve the
problems you are seeing here (i.e. add memory after booting).  It looks
like this is the same issue you are having here, just in a different
part of the kernel.

thanks,

greg k-h
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